# Private Well Chlorine Contact Time Calculator: Check a Chlorination Quote

Source: https://brictale.com/water/filtration/private-well-chlorine-contact-time-calculator
Published: 2026-08-31
Audience: Homeowner
Published by Brictale, a consumer home-intelligence publication. https://brictale.com

## Short answer

Use CT as a quote-check screen, not proof that drinking water is safe. Calculate effective contact time at measured peak flow, multiply it by free chlorine residual at the correct downstream sampling point, and compare the result with the applicable state or manufacturer target. Stop if the quote uses average flow, nominal tank volume, an unverified pressure tank, or an unstated target; route those gaps to the health department, certified laboratory, or qualified installer.

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# Private Well Chlorine Contact Time Calculator: Check a Chlorination Quote

Use this as a quote-check worksheet, not as a drinking-water safety certification. The useful question is not “Does this tank have enough gallons?” It is “At the highest credible flow, how much effective contact time exists after chlorine is injected, what free chlorine residual was actually measured at the correct downstream point, and which rule, engineer, or equipment manual sets the target?”

The screening calculation is:

`T_theoretical (minutes) = contact volume (gallons) ÷ peak flow (gallons per minute)`

`CT_screen (mg-min/L) = free chlorine residual (mg/L) × effective contact time (minutes)`

EPA describes CT as disinfectant residual concentration multiplied by contact time, and says the result is affected by pH, temperature, flow, and substances in the water. [EPA’s ground-water sanitary-survey guidance](https://www.epa.gov/sites/production/files/2016-12/documents/gwr_sanitary_survey_guidance.pdf) treats CT as a system-design and monitoring concept, not a universal private-well pass/fail number. If a proposal gives you only a nominal tank size, average flow, and chlorine-feed setting, the correct outcome is **not validated**.

## 1. What this screen can—and cannot—tell you

A chlorination proposal should make a chain of decisions auditable:

1. Where is chlorine injected?
2. Which vessel or pipe segment is intended to provide contact time?
3. What is the maximum credible flow through that section?
4. What volume is actually available at that flow?
5. How is short-circuiting or poor mixing addressed?
6. Where and how is free chlorine residual measured?
7. What pH, temperature, turbidity, and contaminant demand were assumed?
8. Which state, local-health, engineer, or manufacturer target is being applied?

If those questions have answers, the homeowner can check whether the quote’s math is internally consistent. If they do not, the gap is the finding. A large tank can still be the wrong tank, a high chlorine feed can still be poorly controlled, and a calculated CT can still be irrelevant if it uses the wrong residual or sampling point.

CT does not tell you whether your well is free of nitrate, arsenic, PFAS, volatile chemicals, radionuclides, or other contaminants. It also does not prove that a chlorinator is feeding consistently, that a tank is clean, that the well is sanitary, or that a laboratory result is acceptable. [CDC says private-well owners should use a state-certified laboratory and consult the health department about local contaminants](https://www.cdc.gov/drinking-water/safety/guidelines-for-testing-well-water.html). CDC also says no single home-treatment type protects against every problem and that contaminated well water should not be used for drinking until treatment is completed and testing confirms the result. [See CDC’s treatment guidance](https://www.cdc.gov/drinking-water/safety/guidelines-for-treating-well-water.html).

That limitation matters because continuous chlorination can be proposed for different jobs. It may be intended to provide a residual barrier against bacteria, to oxidize iron, manganese, or hydrogen sulfide before filtration, or to address a recurring microbial problem. Those are not interchangeable design objectives. The required residual, contact time, pretreatment, filtration, sampling, and verification may differ.

### A result vocabulary for this page

Use one of these labels instead of calling a proposal “safe”:

| Screen result | What it means | Safest next step |
|---|---|---|
| **Quote math is internally consistent** | Required inputs are documented, effective detention is supported, the measured residual is from the specified point, and CT meets the applicable target. | Send the worksheet and source documents to the health department or qualified installer for design confirmation and arrange laboratory testing. |
| **Conditionally reviewable** | The arithmetic can be done, but one or more inputs are assumptions: nominal volume, average flow, generic residual, unverified baffling, or an unclear target. | Ask the installer to document the missing input; do not approve based on the calculated number alone. |
| **Not validated** | The target is missing or out of scope, peak flow is not known, residual is not measured, or the pressure tank is being counted without a defensible effective-volume basis. | Pause the decision and route the proposal to the local health department, certified laboratory, or qualified water-treatment professional. |
| **Stop and protect water use** | Residual is absent or below the applicable requirement, contamination is suspected, chemical handling is uncontrolled, or treatment has failed. | Use an alternate safe source as appropriate and obtain professional and health-department direction. Do not try to correct a failed system by guessing at chlorine dose. |

The first row is still only a design-screen result. It is not a certificate that the water is safe to drink.

## 2. Map the treatment train before doing any math

Draw the proposed flow path from the well to the home. A typical continuous-chlorination arrangement may include a well pump, chlorine solution tank, chemical feed pump, injection point, pressure tank, contact tank, optional filtration or activated carbon, and a sampling faucet. The order matters.

[Maine’s continuous-chlorination guidance](https://www.maine.gov/dhhs/mecdc/sites/maine.gov.dhhs.mecdc/files/Continuous%20Chlorination%20Disinfection%20System%20Installation%20Guidance.pdf) identifies a chemical feed pump, chlorine solution tank, free-chlorine residual monitoring kit, and raw-water tap as required features for the small public systems covered by that document. It also shows that the injection arrangement changes depending on whether the chemical pump is tied to the well pump or paced by a flow meter. Use this as a proposal-completeness checklist, not as a private-well rule for every state.

Record these points on the quote:

| Point | What to record | Why it changes the decision |
|---|---|---|
| Raw-water sample point | Faucet or port before chlorine injection, pressure tank, and other treatment | Establishes baseline pH, temperature, turbidity, iron, manganese, sulfur, and microbial or chemical testing. |
| Chlorine injection point | Exact pipe location and whether it is before or after the pressure tank | Defines where contact time begins and whether unchlorinated water can enter the train first. |
| Pressure tank | Bladder or non-bladder; nominal volume; drawdown; location relative to injection | Nominal capacity is not automatically effective detention volume. |
| Dedicated contact tank | Nominal volume, usable water level, internal baffles or mixing design, outlet location | This is usually the component intended to provide controlled detention. |
| Post-contact sample point | Faucet immediately after the contact tank or the point specified by the applicable design | Residual must be tied to the time and location used in the CT calculation. |
| Final-use point | First customer, entry to distribution, or farthest fixture, as applicable | A residual at one point does not describe every point in the home. |
| Optional post-treatment | Carbon, iron filter, sediment filter, UV, or other equipment | A treatment step can consume residual, add pressure loss, or change the water-quality basis. |

{{visual:chlorination-train-and-sampling-points}}

Ohio’s rule is a useful example of why this map should come first. [Ohio Administrative Code Rule 3701-28-15](https://codes.ohio.gov/ohio-administrative-code/rule-3701-28-15) requires disinfectant to be applied before the storage or retention tank to obtain the required contact time, requires a sampling faucet after each disinfection and filtration step, and distinguishes a dedicated disinfection contact tank from other system components. That is Ohio law, not a national design rule.

### Do not silently combine these volumes

Ask the installer to state, in writing, whether each volume is included:

- dedicated contact-tank working volume;
- pressure-tank water volume;
- pipe volume between injection and sampling;
- filter or media-bed volume;
- dead-leg or bypass volume;
- water above or below the normal operating level; and
- any volume that is present only while a pump is off.

The proposal should also state the **effective** detention assumption. “The tank is 120 gallons” describes a nominal label. It does not describe how much water a moving slug occupies, how the inlet and outlet are arranged, or whether portions of the tank short-circuit. EPA explains that contact time is the interval between the dosage point and a downstream sampling point, not simply the time a tank appears full. [See EPA’s definition and sampling discussion](https://www.epa.gov/sites/production/files/2016-12/documents/gwr_sanitary_survey_guidance.pdf).

## 3. Enter the numbers a homeowner can audit

Do not start with the proposed tank. Start with the measured or documented conditions.

### Required input table

| Input | Enter | Evidence to request | If missing |
|---|---:|---|---|
| Peak flow, Q_peak | ___ gpm | Flow test, pump limit, or design calculation showing the maximum credible flow through the treatment train | Do not substitute an average daily flow. Mark the screen not validated. |
| Contact-tank nominal volume | ___ gal | Manufacturer data sheet and model number | Do not estimate from tank height or a photograph. |
| Usable/effective volume basis | ___ gal or T10 ___ min | Manufacturer performance data, engineer calculation, tracer or baffling basis where applicable | Treat nominal volume as theoretical only. |
| Pipe volume included? | yes / no | Pipe size, length, and whether the water path is always active | Exclude uncertain pipe volume until documented. |
| Pressure-tank volume included? | yes / no | Tank model, drawdown, flow path, and professional design basis | Default to no for a conservative homeowner screen. |
| Free chlorine residual, C | ___ mg/L | DPD free-chlorine reading from the specified downstream sampling point, with date and conditions | A feed setting or odor is not a measured residual. Mark not validated. |
| pH | ___ | Meter reading at the stated location, method, date, and calibration status | Do not assume neutral pH. Escalate if CT target depends on it. |
| Water temperature | ___ °C / °F | Measurement during the representative low-temperature condition or stated design basis | Do not assume summer temperature represents winter operation. |
| Turbidity and demand context | ___ | Laboratory or field data for turbidity, iron, manganese, sulfur, ammonia, organics, and other known demand | A residual measured after unknown demand may not represent design conditions. |
| Applicable target | ___ CT; ___ residual; ___ time | State/local rule, health-department approval, engineer design, or exact equipment manual | No target means no pass/fail comparison. |
| Sampling location | ___ | Labeled faucet or port relative to injection, tank, filters, and first use | A result from the wrong point cannot validate the quoted CT. |

EPA’s training guidance defines the relationship between chlorine dose, chlorine demand, and residual: residual is what remains after chlorine reacts with organic and other substances, and demand is not a decorative input. [EPA notes that measured demand can change as contact time increases](https://www.epa.gov/sites/default/files/2019-08/documents/sanitary_survey_learners_guide_508_8.27.19.pdf). A proposal that gives only “inject X ounces per hour” without a residual target and a measurement plan is incomplete.

{{visual:ct-screen-input-map}}

### Calculate theoretical time first

If a proposal claims 120 gallons of contact volume and the measured peak flow is 10 gpm:

`T_theoretical = 120 gal ÷ 10 gpm = 12 minutes`

That is a displacement calculation, not proof that every portion of water receives 12 minutes. If the documented effective detention is 8 minutes, use 8 minutes for the screen:

`CT_screen = 0.5 mg/L × 8 min = 4 mg-min/L`

The units matter. A chlorine residual in ppm is numerically equivalent to mg/L for dilute water, but write the unit the test reports. Do not multiply chlorine dose by tank time when the target is based on the free residual after demand. Do not use total chlorine when the requirement specifies free chlorine.

### Example with an unresolved assumption

Suppose a quote says:

- 150-gallon contact tank;
- 8 gpm “normal” flow;
- 0.5 ppm chlorine setting;
- no pH or temperature;
- no documented tank efficiency;
- residual measured at a kitchen faucet after a carbon filter.

The apparent arithmetic is `150 ÷ 8 = 18.75 minutes`, and `0.5 × 18.75 = 9.375 mg-min/L`. That number looks reassuring but is not a validated CT screen. It uses normal flow rather than peak flow, a feed setting rather than measured residual, nominal tank volume rather than effective detention, and a sample after an unaccounted treatment step. Record it as **not validated**, not as a passing result.

## 4. Treat effective detention as the hard part

The phrase “contact time” can hide three different ideas:

- **Theoretical hydraulic detention:** volume divided by flow.
- **Effective detention:** the time the relevant water actually remains in contact under the design flow and mixing pattern.
- **Verified performance:** evidence that the installed system maintains the required residual and treatment outcome over operating conditions.

These are not interchangeable. A tank can be large on paper and still have a short path from inlet to outlet. A pipe can add volume but be bypassed, intermittently full, or downstream of the sampling point. A pressure tank can hold water while the system is idle but contribute less useful contact when water is being pumped and used.

UGA Extension gives a concrete warning: during simultaneous pumping and household demand, fresh water may bypass water already in the pressure tank, so the pressure tank is usually not adequate as extra contact time. [UGA’s private-system guidance](https://fieldreport.caes.uga.edu/publications/B939/water-quality-and-common-treatments-for-private-drinking-water-systems/) uses a separate intermediate storage tank for a theoretical 10-to-15-minute detention example and says a 10-gpm pump would require at least 100 gallons for 10 minutes of theoretical time. Treat that as a useful warning and example, not an automatic design for your property.

{{visual:pressure-tank-bypass-cutaway}}

UGA’s disinfection guidance shows the same distinction in a different way: contact can occur in a pressure tank, but water may not remain long enough for complete oxidation, which is why a dedicated contact tank may be used. [See UGA’s treatment-device discussion](https://fieldreport.caes.uga.edu/publications/B1487/water-disinfection-methods-and-devices/).

### The pressure-tank question

Put a large “yes/no” box on the quote:

> Is the pressure tank being counted as contact volume?

If yes, ask for all of the following:

1. the tank’s actual water volume, not just total shell size;
2. the drawdown volume at the operating pressure range;
3. the injection point relative to the tank inlet;
4. the outlet and check-valve arrangement;
5. the maximum simultaneous flow used in the design;
6. the effective detention or baffling basis; and
7. the residual sample point used to verify the result.

If the answer is “the pressure tank is 44 gallons,” that is not enough. If the answer is “the contact tank is 120 gallons,” ask whether that is nominal, working, or effective volume. If the installer cannot separate those terms, stop the comparison and ask for a revised design sheet.

### Short-circuiting and mixing

A tank is not a magical stopwatch. Inlet placement, outlet placement, internal baffles, diffusers, turnover, air, temperature, and flow regime can alter the path. Ohio’s rule requires the dedicated contact tank for the covered private systems to be designed to reduce short-circuiting. [The rule’s contact-tank paragraph](https://codes.ohio.gov/ohio-administrative-code/rule-3701-28-15) is a state example of a design feature that generic gallon calculators omit.

Ask whether the manufacturer supplies an effective-volume, baffling, or T10 basis for the exact model. If the answer is no, retain the theoretical calculation as a lower-confidence screen and do not convert it into an approval. A qualified designer may use a method that is not available to a homeowner; your job is to identify whether the method exists and whether it applies to the proposed model and flow.

## 5. Compare CT with the right target

There is no single U.S. homeowner CT target that can be pasted onto every private well. The target may depend on state law, system classification, the contaminant or organism of concern, the treatment objective, pH, temperature, residual type, filtration, and the exact equipment.

### Ohio is an example, not a national rule

Ohio Rule 3701-28-15 says that covered private water systems must meet calculated peak demand or maximum pump flow and be capable of at least 10 gpm. For one-, two-, or three-family dwellings, it specifies a 120-gallon-per-household minimum contact tank unless a smaller approved design ensures adequate contact time; it also requires short-circuiting reduction. For certain larger service configurations, it specifies at least eight minutes at peak demand.

For chlorination, that same Ohio rule states that sufficient chlorine must satisfy demand, CT must be at least 4, and free chlorine residual must be at least 0.4 mg/L after eight minutes of contact. Those values belong to Ohio’s rule and its scope. They are valuable when the home is in Ohio and the system fits the rule; they are not a nationwide answer and may not address every treatment objective. [Read the current Ohio rule directly](https://codes.ohio.gov/ohio-administrative-code/rule-3701-28-15).

Use a target table like this:

| Target source | What to capture | How to use it |
|---|---|---|
| State or local rule | State, county, rule number, effective date, system classification, exact clause | Apply only if the property and system fall within that rule. Keep the link with the quote. |
| Health-department approval | Agency, approval or permit reference, design conditions | Ask what flow, residual, pH, temperature, and sampling point the approval assumes. |
| Qualified engineer or installer design | Signed or attributable design basis, target CT, residual, temperature, pH, demand, and effective detention | Check that the equipment model and operating conditions match the design. |
| Manufacturer manual or performance data | Exact model, rated flow, tank volume, mixing/baffling basis, residual or contact requirements | Do not replace the manual with a similar-looking tank’s data. |
| Generic extension example | Source, purpose, and limitations | Use for questions to ask, not as a pass/fail target. |

Maine’s guidance illustrates this scope discipline. For the small public systems covered by its document, it calls for a residual monitoring kit, directs readings to the entry point immediately after the contact tank, requires a low-range DPD free-chlorine test kit rather than a pool kit, and gives a 0.2-to-0.7 mg/L target range. It also says pH, temperature, and peak flow are needed to calculate contact-tank volume. [Read the Maine guidance](https://www.maine.gov/dhhs/mecdc/sites/maine.gov.dhhs.mecdc/files/Continuous%20Chlorination%20Disinfection%20System%20Installation%20Guidance.pdf). Use those details to ask better questions; do not label them your state’s requirement unless your authority says so.

{{visual:state-target-scope-comparison}}

### Use the conservative condition

If the target varies with temperature, use the condition the design actually covers. EPA says chlorine is less effective at lower temperatures and that pH changes the relative amount of the more effective hypochlorous acid form. [EPA’s ground-water guidance explains the temperature and pH dependence](https://www.epa.gov/sites/production/files/2016-12/documents/gwr_sanitary_survey_guidance.pdf). UGA similarly lists temperature, pH, turbidity, and dissolved constituents as factors that affect chlorination. [UGA’s disinfection guidance](https://fieldreport.caes.uga.edu/publications/B1487/water-disinfection-methods-and-devices/) explains why iron, manganese, hydrogen sulfide, organic matter, and ammonia can consume chlorine or interfere with contact.

If the proposal gives a target at pH 7 and 20°C but the well operates at a higher pH and colder groundwater, ask the designer to show the adjustment. Do not “fix” it by adding chlorine yourself. A higher feed setting can create taste, odor, byproduct, handling, or control problems and may still fail to solve the underlying water-quality issue.

## 6. Check the measurement and maintenance plan

The quote is not complete until it says how the system will be measured after installation. A chlorine solution tank size and a chemical pump stroke setting are not verification.

### Residual measurement

Ask for:

- free chlorine or total chlorine, clearly identified;
- units, usually mg/L or ppm;
- test method and kit range;
- exact sample faucet or port;
- whether the sample is before or after the contact tank;
- whether it is before or after carbon or other treatment;
- date, time, flow condition, pH, and temperature; and
- the expected acceptable range or minimum.

Maine’s guidance is unusually clear about this: residual readings are taken at the entry point right after the contact tank, with a low-range DPD free-chlorine kit, and should not be replaced by a pool test kit for the systems covered by that document. That is a useful model for documentation even where Maine’s rule does not apply.

UGA says free chlorine residual should be checked periodically with a free chlorine test kit. [UGA’s private-well treatment guidance](https://fieldreport.caes.uga.edu/publications/B939/water-quality-and-common-treatments-for-private-drinking-water-systems/) also describes the residual as the chlorine left after chlorine demand has been satisfied. A reading taken at a distant faucet after carbon filtration may answer a different question than a reading immediately after the contact tank.

### Demand and water quality

A chlorine feed can be correct one day and inadequate another day if demand changes. Ask whether the design considered:

- iron and manganese;
- hydrogen sulfide or sulfur odor;
- ammonia or organic nitrogen;
- organic matter or color;
- turbidity, sand, or suspended solids;
- pH and temperature range;
- seasonal changes or well-yield changes; and
- what happens when a filter is backwashing or a bypass is open.

EPA notes that substances such as sand, dirt, iron, manganese, and other groundwater constituents can hide organisms from chlorine contact or reduce germicidal effectiveness. UGA explains that chlorine readily combines with several dissolved components and that pretreatment or filtration may be necessary for the treatment objective. A residual test alone is not a laboratory diagnosis of those conditions.

### A homeowner-safe observation log

You may record readings from an existing, safe sampling faucet if the installer or kit instructions say how to do it. Keep the log with the quote:

| Date/time | Faucet and location | Flow condition | Free residual | pH | Temperature | Notes |
|---|---|---|---:|---:|---:|---|
| ___ | ___ | low / typical / peak test | ___ mg/L | ___ | ___ | odor, color, filter status |
| ___ | ___ | low / typical / peak test | ___ mg/L | ___ | ___ | tank level or alarm observed |
| ___ | ___ | low / typical / peak test | ___ mg/L | ___ | ___ | carbon/filter/bypass status |

Do not interpret a clear glass, normal taste, or absent odor as a microbiological result. CDC’s private-well guidance places responsibility for testing with the well owner because private wells are not monitored like public systems. Use the local health department and a state-certified laboratory for the water-quality question.

### Maintenance questions

Request a written schedule for:

1. chlorine solution preparation, concentration, labeling, and storage;
2. free-residual testing frequency and acceptable range;
3. chemical feed pump inspection and calibration;
4. flow-meter or pump interlock verification;
5. contact-tank inspection, cleaning, drain, and venting;
6. filter or carbon replacement and pressure-drop limits;
7. alarm or low-chemical response;
8. sampling after service, bypass, power loss, or plumbing changes; and
9. who is called when residual is low or absent.

Maine’s guidance says a chemical feed pump should activate with the well pump in one configuration and be flow-paced when multiple wells or a variable-speed pump are used. It also calls for residual records and occasional checks at far reaches of the distribution system for the systems it covers. Those details are important because a fixed dose can drift out of proportion to flow. Ask your installer which control strategy applies to your pump and what evidence proves it works.

## 7. Stop conditions, professional handoff, and safe next action

Stop the quote comparison and obtain qualified help if any of these are true:

- there is no stated state, local, engineer, or exact-manual target;
- peak flow is replaced by average daily flow or an unverified “normal” flow;
- the proposal counts a pressure tank without a documented effective-volume basis;
- the tank is described only by nominal gallons;
- residual is a chlorine-feed setting, odor, or a result from an unspecified faucet;
- the test is total chlorine when the target requires free chlorine;
- pH, temperature, or known chlorine demand are omitted from a target that depends on them;
- the sampling point is after a carbon filter or other treatment but the design assumes a pre-filter residual;
- the proposal has no plan for low residual, empty chemical tank, power loss, flow-meter failure, or bypass;
- a lab report shows bacteria or a chemical of health concern; or
- the installer wants you to alter feed settings without a documented procedure and verification test.

Use alternate safe water and contact your local health department if contamination is suspected. CDC says not to drink well water containing harmful germs or chemicals until the water is treated and testing shows that treatment worked. Chlorine can address some microbial risks, but [CDC explains that treatment methods are contaminant-specific](https://www.cdc.gov/drinking-water/about/about-home-water-treatment-systems.html); chlorine is not a general-purpose removal method for chemical contamination.

### Safety boundary for homeowners

A homeowner may photograph labels, read an existing gauge, record the model and serial number, observe a labeled sampling faucet, and organize laboratory and quote documents when those actions can be done without opening equipment or changing the system. Follow the test-kit and installer instructions for any sample collection.

Do not open energized controls, test live wiring, open a well or well cap, pull a pump, enter a tank or other confined space, open pressurized equipment, disconnect chemical tubing, mix or transfer concentrated chlorine, or change pump stroke, feed rate, valves, wiring, or pressure settings unless a specific written procedure from a qualified professional makes the action demonstrably safe. Assign electrical, well, chemical-feed, pressurized, confined-space, and code-related work to a qualified professional. Keep chlorine products away from incompatible chemicals and follow the product label and safety data sheet.

### The handoff packet

Give the health department, certified laboratory, or qualified installer one packet containing:

- the complete quote and every model number;
- a one-line flow diagram with injection, pressure tank, contact tank, filters, and sample points;
- measured peak flow and how it was obtained;
- nominal and effective contact-volume information;
- the answer to whether pressure-tank volume is counted;
- free-chlorine results with method, location, date, time, and flow condition;
- pH and temperature readings and their locations;
- laboratory results for bacteria and relevant local contaminants;
- the stated treatment objective;
- the exact state or local rule, approval, or manual target; and
- the proposed maintenance, alarm, bypass, and failure-response plan.

Ask the professional to return the calculation with units, assumptions, effective detention basis, and the condition under which it applies. If the professional cannot say what would make the result fail, the proposal is not yet auditable.

The homeowner decision is therefore simple but deliberately bounded: calculate the quoted CT only after identifying the right flow, residual, effective detention, water chemistry, and target; label the result as quote math rather than water safety; and stop when any of those foundations are missing. That is the useful outcome of a private-well chlorine contact-time screen.

## Evidence

- [U.S. EPA — Sanitary Survey Guidance Manual for Ground Water Systems](https://www.epa.gov/sites/production/files/2016-12/documents/gwr_sanitary_survey_guidance.pdf) — EPA guidance for ground-water systems and sanitary surveys. It supports the CT formula and the variables that affect disinfection; it does not create a universal private-well homeowner target.
- [U.S. EPA — Sanitary Survey Guidance Manual for Ground Water Systems](https://www.epa.gov/sites/production/files/2016-12/documents/gwr_sanitary_survey_guidance.pdf) — EPA guidance describing the meaning of contact time, sampling location, and peak-flow evaluation. Applicability and required monitoring remain state- and system-specific.
- [U.S. EPA — How to Conduct a Sanitary Survey of Drinking Water Systems](https://www.epa.gov/sites/default/files/2019-08/documents/sanitary_survey_learners_guide_508_8.27.19.pdf) — EPA sanitary-survey training guidance. It supports separating chlorine dose, demand, and measured free residual; it is not a private-well chemical-dosing prescription.
- [Ohio Administrative Code Rule 3701-28-15 — Continuous disinfection, continuous filtration, cyst reduction filtration and point of entry water treatment](https://codes.ohio.gov/ohio-administrative-code/rule-3701-28-15) — Ohio private-water-system rule only. The peak-demand and 10-gpm provisions must not be generalized as a nationwide private-well requirement.
- [Ohio Administrative Code Rule 3701-28-15 — Continuous disinfection, continuous filtration, cyst reduction filtration and point of entry water treatment](https://codes.ohio.gov/ohio-administrative-code/rule-3701-28-15) — Ohio-specific design and installation requirements. The 120-gallon, eight-minute, and short-circuiting language is an example of a jurisdictional target, not a U.S.-wide rule.
- [Ohio Administrative Code Rule 3701-28-15 — Continuous disinfection, continuous filtration, cyst reduction filtration and point of entry water treatment](https://codes.ohio.gov/ohio-administrative-code/rule-3701-28-15) — Ohio-specific continuous-chlorination requirements. These numbers cannot be used as a nationwide or contaminant-independent pass/fail threshold.
- [University of Georgia Extension — Water Quality and Common Treatments for Private Drinking Water Systems](https://fieldreport.caes.uga.edu/publications/B939/water-quality-and-common-treatments-for-private-drinking-water-systems/) — University of Georgia Extension example and recommendation for private drinking-water systems. The theoretical example is not an engineering approval or a universal tank-sizing rule.
- [University of Georgia Extension — Water Quality and Common Treatments for Private Drinking Water Systems](https://fieldreport.caes.uga.edu/publications/B939/water-quality-and-common-treatments-for-private-drinking-water-systems/) — UGA Extension's general private-system discussion. The values are quoted as that source's recommendation and are not substituted for a local rule, manufacturer target, or contaminant-specific design.
- [University of Georgia Extension — Water Disinfection Methods and Devices](https://fieldreport.caes.uga.edu/publications/B1487/water-disinfection-methods-and-devices/) — University of Georgia Extension explanation of chlorination chemistry and treatment interference. It supports collecting water-quality context, not a claim that chlorine alone solves every contaminant.
- [Maine Drinking Water Program — Continuous Chlorination Disinfection System Installation Guidance](https://www.maine.gov/dhhs/mecdc/sites/maine.gov.dhhs.mecdc/files/Continuous%20Chlorination%20Disinfection%20System%20Installation%20Guidance.pdf) — Maine guidance for small public water systems. It is useful for identifying proposal inputs and components, but it is not a national private-well rule.
- [Maine Drinking Water Program — Continuous Chlorination Disinfection System Installation Guidance](https://www.maine.gov/dhhs/mecdc/sites/maine.gov.dhhs.mecdc/files/Continuous%20Chlorination%20Disinfection%20System%20Installation%20Guidance.pdf) — Maine-specific small-public-system installation and monitoring guidance. The sampling point, test method, and range should not be presented as the requirement for every private well.
- [CDC — Guidelines for Testing Well Water](https://www.cdc.gov/drinking-water/safety/guidelines-for-testing-well-water.html) — General CDC private-well testing guidance. It establishes a testing and escalation boundary, not a validation method for a chlorine contact tank.
- [CDC — Guidelines for Treating Well Water](https://www.cdc.gov/drinking-water/safety/guidelines-for-treating-well-water.html) — General CDC guidance for private-well treatment and contaminated wells. It supports the article's prohibition against treating a CT screen as proof of potable water.