Updated: May 2026
Testing your private well or semipublic well water provides important information about water quality and is the best way to ensure your water supply is safe to use. It can also identify nuisance contaminants such as iron and manganese, and determine their levels. The information below is intended to help well owners decide what to test for and how often. These are general guidelines and may not cover all situations.
Regular testing is important because water quality can change over time. Routine testing also creates a record of water quality that can help identify and address future problems. Owners of private and semipublic wells are responsible for the quality of their water and are typically not required to test. However, testing is strongly recommended even if no issues are suspected, as it is the only way to confirm that water is safe to drink.
It is also highly recommended to test well water when purchasing a home so informed decisions can be made. A good time to test is after periods of heavy rain, typically in the spring or fall.
What to Test For? How Frequently to Test?
Table 1 lists the tests recommended for all private wells even if you do not notice any problems with your water. Table 3 lists water quality issues you might encounter and what tests you should perform if you have a particular issue. Whenever you notice a change in the taste, color, odor, or clarity of your water, contact your Local Health Department or the Connecticut Department of Public Health (CT DPH), Private Well Program for assistance.
Table 1. Recommended Tests for All Private Wells
| Test(s) | When? | Why? |
| Basic Indicators (see Table 2 below) | Every Year Also any time there is repair work to the well, pump or water pipes, or if your well head was flooded. |
Provides a general indication of water quality. Required for all new wells. Some basic indicators above their acceptable limit are associated with health concerns. |
| Lead (2 samples; first draw & flushed samples should be collected when testing for lead) | At Least Once Also when planning a pregnancy or have a child under the age of 6 in the home; or, if your water is considered corrosive, test every 3-5 years. |
Lead can leach from your home’s plumbing (pipes, faucets, valves, etc.) system. Corrosive water leaches lead more readily. Lead above the acceptable limit is associated with health concerns. Young children are especially susceptible to harmful effects from lead exposure. |
| Arsenic, Uranium, Radon | At Least Once Ideally, repeat test every 5 years |
Arsenic, Uranium, Radon Arsenic, uranium and radon are naturally occurring in groundwater in some areas of CT and are associated with health concerns above their acceptable limit. Private wells with high levels have been found sporadically around CT, and levels may fluctuate. |
| Volatile Organic Compounds (VOCs) | At Least Once More often if a problem is identified or suspected |
Gasoline, oil, solvents or industrial chemicals spilled or leaked on the ground could get into your well water. VOCs above their acceptable limit are associated with health concerns. |
| Fluoride | Every 5 years when a child under 12 is present | Fluoride can occur naturally in wells throughout CT. A child’s permanent teeth can become discolored from excess fluoride. Too little fluoride can increase risk of tooth decay. Your child’s dentist may advise you about the fluoride level in your well water. |
Table 2. Basic Indicators Test
| Parameter | Applicable Drinking Water Standard* | Drinking Water Standards |
| Total Coliform Bacteria | None Present |
US EPA Maximum Contaminant Levels (MCLs) *Drinking water standards may be based on aesthetics or on associated health risk. If your water exceeds a drinking water standard, contact your Local Health Department or the CT DPH Private Well Program for assistance. For more information on drinking water standards refer to the links above. |
| Nitrate | 10 milligrams/liter (mg/L) | |
| Nitrite | 1 mg/L | |
| Sodium | 100 mg/L | |
| Chloride | 250 mg/L | |
| Iron | 0.3 mg/L | |
| Manganese | 0.05 mg/L (Based on Aesthetics) 0.3 mg/L (Based on Health Concerns) |
|
| Hardness | 0-60 = Soft 61-120= Moderately Hard 121-180= Hard >181= Very Hard |
|
| Turbidity | Less than 5 standard units (SU) | |
| pH | 6.5 - 8.5 SU |
|
| Sulfate | 250 mg/L | |
| Apparent Color | Less than 15 SU | |
| Odor | Less than 2 |
Table 3. Private Well Water Quality Issues and Recommended Associated Test (Troubleshooting)
| Water Quality Issue | Possible Cause(s) | Recommended Water Test(s) |
| Low pH (less than 6.5) | Generally, naturally occurring | Hardness, Alkalinity, Sulfate, Lead, Copper, Cadmium, Zinc |
| Buildup of limescale (off-white chalky solids) on hot water plumbing, fixtures, kettles, etc. Reduced soap lathering. | Hardness is caused by the amount of mineral content dissolved in water, generally made up of calcium and magnesium. | Hardness |
| Blue or greenish stains on plumbing, fixtures or laundry. Plumbing leaks and pin hole leaks. | Corrosive water may be influenced by pH, hardness level, alkalinity, chloride level, dissimilar metals in plumbing, etc. | pH, Hardness, Alkalinity, Sulfate, Chloride, Sodium, Lead, Copper, Cadmium, Zinc |
| Rust-colored water, rust stains on clothing and plumbing fixtures, rust coating in toilet tank, foul odor | Iron, Manganese, Iron Bacteria | Iron, Manganese, Iron Bacteria |
| Yellow, brown or blackish stains on plumbing fixtures, yellow or brown staining to laundry | Manganese, Iron/Manganese Bacteria, Sulfur Bacteria | Manganese, Iron, Iron/Manganese Bacteria |
| Rotten egg odor, musty or swampy odor, tarnished copper and silverware | Hydrogen sulfide gas, high sulfates, sulfur bacteria, iron/manganese bacteria | Odor, Hydrogen Sulfide, Sulfate, Iron Bacteria, Iron, Manganese, Sulfur Bacteria, Coliform Bacteria |
| Cloudy, Turbid, Muddy Water | Silt, Sediment, microorganisms | Turbidity, Coliform Bacteria, Check Well Construction with an expert |
| Chemical, fuel or fruity odor | Leaking underground fuel tank, gas station fuel spill, industrial chemical spill, road runoff | Volatile Organic Compounds (VOCs) |
| Nitrates exceed 10 mg/L Nitrites exceed 1 mg/L | Fertilizer runoff, malfunctioning septic system | Pesticides* (refer to note below regarding testing for pesticides), Coliform Bacteria |
| Radon in air exceeds 4 pCi/L, or Uranium in water exceeds 30 ug/L | Naturally occurring uranium in bedrock | Uranium, Radium, Radon |
| Recurrent gastrointestinal illness | Human or animal waste contaminating well, cracked well casing, flooded well, malfunctioning septic system | Coliform Bacteria, Nitrates, Nitrites |
| Bitter, metallic taste | Corrosive (low pH) water | pH, Lead, Copper |
| Salty, brackish taste | Road salt runoff, nearby salt storage, well near salt water, improper setting on water softener | Chloride, Sodium, Total Dissolved Solids |
| Well within 1/4 mile of current or former orchard or farmland | Agricultural and/or arsenic-based pesticides get into well | Nitrates, Arsenic, Pesticides* (ask for EPA Method 505) |
| Well within 1/4 mile of commercial or industrial area | Gasoline, oil, solvents leaked or spilled on the ground get into well | Volatile Organic Compounds (VOCs) |
| Well flooding, ponding around well | Heavy rains, poor drainage around well | Coliform Bacteria, Basic Indicators |
| House foundation treated for termites before 1990 | Termite pesticides can leach into well water | Pesticides* dieldrin and chlordane |
| Noticeable change in taste, color, odor, or clarity of your water. | Unknown | Contact your local health department or CT DPH Private Well Program |
*Contact your Local Health Department, CT Dept. of Energy and Environmental Protection, or CT DPH Private Well Program for advice regarding whether you should additionally test for pesticides.
Private Water Supplies
In accordance with Section 19a-37 of the Connecticut General Statutes, testing is required for all new wells. However, the required tests do not cover all contaminants. Water tests done during home purchases are usually required by the bank providing the mortgage. Contrary to common belief, such tests are not required by law and do not necessarily cover all contaminants.
Because this publication provides general guidelines that are not all inclusive it may be recommended to check with your Local Health Department to find out whether there are water quality problems specific to your area. It is also a good idea to ask your neighbors whether they have had water quality problems. The Connecticut Department of Public Health (DPH) Private Well Program is another resource for questions about private well testing. DPH’s Environmental and Occupational Health Hazards Program is a resource for questions about safe limits of chemicals in water and health concerns. Contact information is provided at the end of this document.
What If I Already Have a Treatment System in My Home?
If you have water treatment equipment in your home, you should monitor whether the treatment system is doing its job by testing for the specific contaminant(s) that the system is treating for. Be aware that water treatment systems are designed for specific contaminants and will not necessarily remove all contaminants. Periodically test your water quality before and after treatment to be sure the system continues to work properly and to monitor any fluctuation in your raw water quality. Refer to our guidance: Questions to Ask When Purchasing Water Treatment Equipment for Your Home for more information about treatment.
How Do I Get My Water Tested?
You can have your water tested at any state-certified water testing laboratory. A current list of certified labs approved to test drinking water is available on the DPH Environmental Laboratory Certification Program website. Be sure the laboratory you choose is certified to test drinking water for the specific contaminants you are concerned about.
In most cases, you can collect tap water samples yourself, although some laboratories may offer services to send a technician to collect them upon request. If you collect the samples yourself, it is important to carefully follow the laboratory’s instructions, as sampling methods vary depending on the test.
For example, testing contaminants such as lead and copper may require water to sit undisturbed in the pipes for at least six hours, to ensure the first draw of water is collected. Other tests may require the water to be flushed for a set period before sampling. Some contaminants also require special bottles and handling procedures.
Cleanliness is essential—nothing should come into contact with the opening of the bottle or the inside of the cap except the water sample itself. Timing is also important, as some contaminants can change or break down over time. Most samples must be kept cool during transport to the lab. To ensure accurate results, samples should be delivered to the laboratory within the specified timeframe provided in the instructions.
Keep Records
Keep a record of all your water test results with dates. A change in the concentration of a contaminant may indicate that a water quality problem is developing. Additionally, by comparing test results over time, you may find that a change in treatment is necessary or that a treatment device is not functioning properly.
Understanding Your Water Test Results
There are federal and state criteria for many of the substances that you might find in your private well water. These criteria indicate the concentration above which might not be safe to consume or use or might have an aesthetic effect on your water such as imparting a taste, odor or color.
DPH sets state drinking water criteria specifically for private wells, called Action Levels. Action levels are developed to protect you from health risks. Federal drinking water criteria to protect your health are set by the US Environmental Protection Agency (EPA) and are called Maximum Contaminant Levels (MCLs). You should compare the results of your private well tests to these criteria to determine whether the water is safe. If any of your water quality test results are higher than an Action Level or an MCL, you should:
- Retest the water to confirm the exceedance
- Stop drinking the water until the issue is resolved
- Contact your Local Health Department or the CT DPH Private Well Program for specific guidance
- Consider installing treatment to remove the contaminant(s) from your water: refer to DPH's Questions to Ask When Purchasing Water Treatment Equipment for Your Home for more information about treatment
Refer to CT DPH’s Chemical Contaminants in Private Wells fact sheet for more information on how drinking water criteria are set.
EPA also sets drinking water criteria to protect you from aesthetic concerns such as taste, color and odor. These criteria are called Secondary Maximum Contaminant Levels (SMCLs). Secondary contaminants themselves do not necessarily present a health risk but could be an indication that your water has problems that may pose a health risk. For example, if the pH of your water is too low it may cause your water to be corrosive. Corrosive water can leach metals like lead and copper more readily from pipes and fixtures. High levels of lead in your water does pose a health risk, particularly for young children.
Results of a Basic Indicators Test should be compared with the appropriate limits shown in Table 2 in this fact sheet. However, be aware that some of the parameters in the Basic Indicators Test are based on aesthetic concerns and some are based on health risk. If your water tests results exceed any of the limits on the Basic Indicators Test, contact your Local Health Department or the DPH, Private Well Program for advice regarding whether you should stop drinking the water.
Protect Your Well
You can help protect your private well water quality by paying careful attention to what you do around your well. Pay attention to nearby neighboring activities as well. Regular testing and good practices to prevent contamination can help ensure that your well supplies you and your family with good quality drinking water. Here are some important ways you can protect your drinking water well:
- Locate new wells far from any potential contamination sources
- Hire a professional to construct new wells or to periodically inspect existing wells
- Use backflow prevention devices on outdoor hose bibb spigots
- Properly seal abandoned and unused wells
- Never flush gasoline, oils, chemicals, or solvents down the sink or toilet to a septic system
- Inspect and properly maintain your septic system
- Keep livestock and pet waste away from your well
- Do not allow surface wash, especially from road, driveway or roof runoff to collect around your well
- Do not mix or use fuels or other hazardous materials near your well
- Do not use or over apply products used to melt snow and ice, fertilizers, pesticides and herbicides near your well
- Do not allow waste oils or gasoline to get into soil (never perform automotive repair on exposed soil.)
- Make sure home heating tanks are above ground or in basement, and periodically check for leaking
- Test your private well water according to the recommendations listed in this publication
- Refer to Private Wells: Best Management Practice Checklist for more information
For More Information
CT Department of Public Health:
- Private Well Program: (860) 509-8401
- Environmental & Occupational Health Hazards Program: (860) 509-7740
Find your Local Health Department
CT Department of Energy & Environmental Protection:
- Remediation Division (for man-made contamination): (860) 424-3705
For more information regarding specific private well water contaminants, water treatment technologies and guidance, please refer to the CT DPH, Private Well Program: Publications and Fact Sheets page.