Family Survival

Tools / water standards

Water purity standards

The EPA's National Primary Drinking Water Regulations are legally enforceable limits and treatment rules for public water systems, the utility that sends you a water bill. ⁠[1] They do not apply to private wells, so if you have a well, testing it is up to you. ⁠[2] Each contaminant has two numbers: a health goal (MCLG), which is not enforced, and a legal limit (MCL or "action level"), which is set as close to that goal as treatment and cost allow. For lead, arsenic, PFOA, PFOS, uranium and radium the health goal is zero, so a result under the legal limit does not mean "no risk". ⁠[1]

Reviewed 2026-09-21 · 13 contaminants · 61 sources

01 The limits

An MCL (maximum contaminant level) is the legal limit for public water systems. An action level is the level that makes a utility take steps, such as treatment or replacing pipes.

ContaminantLimitWhy it matters
Nitrate (measured as nitrogen) 10 mg/L
MCL		 Babies under six months who drink water above this limit can become seriously ill, with shortness of breath and blue-baby syndrome, and can die if not treated. Boiling makes nitrate more concentrated.
Current as of September 2026.[1]
Nitrite (measured as nitrogen) 1 mg/L
MCL		 Same risk to babies under six months as nitrate, at one tenth the level.
Current as of September 2026.[1]
Arsenic 0.010 mg/L (10 ppb)
MCL		 The health goal is zero. Arsenic causes skin damage and circulatory problems and may raise cancer risk. The 10 ppb limit is what can be enforced, not a safe level. It occurs naturally in rock, so wells are the main concern.
Current as of September 2026. The limit dropped from 50 ppb to 10 ppb in 2001. ⁠[3][1]
Lead Action level 0.015 mg/L (15 ppb), dropping to 0.010 mg/L (10 ppb) on November 1, 2027
Action level (treatment technique)		 The health goal is zero. EPA says there is no safe level of lead. In children it can delay physical and mental development. In adults it causes kidney problems and high blood pressure. The action level is not a safety limit. It is the point at which a utility must do more to control corrosion, if more than 10% of the homes it samples are above it. Boiling does not remove lead.
Current as of September 2026. Under today's Lead and Copper Rule, the action level is 15 ppb. ⁠[4] EPA's final Lead and Copper Rule Improvements (LCRI, October 2024) lower it to 10 ppb from November 1, 2027. The LCRI also requires utilities to replace most lead service lines within 10 years. ⁠[5] Water utilities have challenged the LCRI in the D.C. Circuit (American Water Works Association v. EPA). EPA is defending the rule: in a February 20, 2026 court filing it defended the 10-year replacement requirement. ⁠[6] Briefing is complete. As of NRDC's April 23, 2026 update, oral argument was expected in fall 2026. ⁠[7] We found no court decision, stay or proposal to delay the LCRI as of September 21, 2026. EPA's drinking water table, updated August 31, 2026, still lists the November 1, 2027 date. On August 21, 2026, EPA published guidance to help utilities meet the LCRI's lead pipe replacement requirements. ⁠[8][1]
Copper Action level 1.3 mg/L
Action level (treatment technique)		 In the short term it causes stomach upset. Over the long term it can damage the liver or kidneys. Copper usually comes from corroding household pipes.
Current as of September 2026.[1]
Total coliform and E. coli (Revised Total Coliform Rule) E. coli: health goal zero; total coliform: treatment technique
MCL (E. coli) and Treatment technique (total coliform)		 Coliforms are usually harmless in themselves. They are a warning sign that germs from sewage or animal waste may have got in. E. coli points to fecal contamination specifically. Under the Revised Total Coliform Rule, a utility that finds coliforms must look for the cause and fix it. An E. coli violation must be reported to the public.
Current as of September 2026. The Revised Total Coliform Rule has applied to public water systems since April 1, 2016.[9]
Fluoride 4.0 mg/L (secondary guideline 2.0 mg/L)
MCL (plus a non-enforceable secondary standard)		 Above 4.0 mg/L it can cause bone disease (pain and tenderness). The 2.0 mg/L secondary guideline is meant to prevent children's teeth from becoming mottled or discolored where natural fluoride is high.
In force at 4.0 mg/L as of September 2026, but EPA is reviewing it early. On August 3, 2026, EPA released the protocol for a new fluoride health assessment. The limit has not been changed. ⁠[10][1]
Uranium 30 µg/L
MCL		 The health goal is zero. Uranium raises cancer risk and harms the kidneys. It occurs naturally in granite and other crystalline rock, so it shows up in some bedrock wells.
Current as of September 2026.[1]
Radium-226 and radium-228 (combined) 5 pCi/L
MCL		 The health goal is zero. Radium builds up in bone and raises lifetime cancer risk. It comes from natural rock deposits.
Current as of September 2026.[1]
PFOA (a PFAS "forever chemical") 4.0 ppt (ng/L)
MCL (final April 2024; compliance date proposed to move)		 The health goal is zero. Studies link PFAS to higher cholesterol, changes in liver enzymes, a weaker vaccine response in children, lower birth weight and some cancers.
The limit is final and legally in effect. EPA finalized it on April 10, 2024. Utilities must finish first-round monitoring by 2027 and meet the limit by 2029. On May 18, 2026, EPA proposed keeping the 4.0 ppt limit but letting eligible systems apply for two more years, to April 2031. That proposal is not final. Public comment closed July 20, 2026. ⁠[11] Utilities' challenge to the rule (AWWA v. EPA, D.C. Circuit No. 24-1188) is still pending. EPA is defending the PFOA and PFOS limits. Oral argument was scheduled for September 18, 2026, and no decision had been reported as of September 21, 2026. ⁠[12] ⁠[13][14]
PFOS (a PFAS "forever chemical") 4.0 ppt (ng/L)
MCL (final April 2024; compliance date proposed to move)		 The health goal is zero, for the same reasons as PFOA.
Same as PFOA. The limit is final and in effect, with compliance due by 2029. The May 18, 2026 proposal would let eligible systems apply to take until April 2031. It is still pending as of September 21, 2026.[14]
PFHxS, PFNA and HFPO-DA ("GenX") 10 ppt each
MCL (final April 2024; proposed for rescission May 2026)		 Other PFAS chemicals that were given their own limits in the 2024 rule.
Still legally in effect, but EPA has proposed removing these limits. On May 18, 2026, EPA proposed rescinding the limits for PFHxS, PFNA and HFPO-DA, and the Hazard Index. EPA says the 2024 rule skipped a step the Safe Drinking Water Act requires. Public comment closed July 20, 2026. The rescission is not final. EPA's page says it will look at regulating these chemicals again later, and that the outcome could be stricter. The D.C. Circuit refused to throw out these limits early: it denied EPA's motion for partial vacatur on January 21, 2026 ⁠[15], and denied its motion to sever and pause that part of the case on March 19, 2026. ⁠[16] So the court will rule on all the challenged limits.[17]
PFAS mixtures (two or more of PFHxS, PFNA, HFPO-DA and PFBS) Hazard Index of 1 (unitless)
MCL (final April 2024; proposed for rescission May 2026)		 Adds up the combined effect of several PFAS found together. Each chemical's level is divided by its health-based level, and the total must not go above 1.
Same status as PFHxS, PFNA and HFPO-DA. It is in effect, but the May 18, 2026 proposal would rescind it. That proposal is not final as of September 21, 2026.[14]

02 What boiling, bleach, and filters remove

MethodRemoves or killsDoes not remove
BoilingKills germs. CDC calls boiling the best way to kill germs in water.Chemicals. Boiling doesn't remove lead, and it makes nitrate worse: some water boils off and the nitrate stays behind, so it becomes more concentrated. Boiling or disinfecting can't make water safe if it contains fuel, toxic chemicals or radioactive material.[18]
Household bleach and other chemical disinfectantsKills most germs, including bacteria and viruses.Works less well than boiling against the parasites Cryptosporidium and Giardia. Iodine and chlorine tablets won't kill Cryptosporidium; chlorine dioxide tablets will if you follow the directions. Does nothing about chemicals.[18]
Portable (backpacking) filtersParasites, if the absolute pore size is 1 micron or smaller. Bacteria, if it is 0.3 micron or smaller.Viruses. After filtering, add a chemical disinfectant to kill viruses and bacteria.[18]
Pitcher, fridge and faucet filters (activated carbon)Mainly improve taste and smell. Some also remove heavy metals such as lead. Look for 'certified to remove lead' on the label. Some carbon filters are certified to reduce PFAS (NSF/ANSI 53).Most are not designed to remove germs. Filters remove only what their certification lists.[19]
Certified filters: what the NSF/ANSI numbers mean42: taste and odor and chlorine. 53: a contaminant with a health effect, including PFAS reduction and cyst reduction, if the product is certified for it. 58: reverse osmosis. 62: distillation. 401: up to 15 'emerging' contaminants. 55: ultraviolet (UV). 44: water softeners.Certification doesn't mean a filter removes everything. Check that the product is certified for the specific contaminant you care about. EPA notes that, as of April 2024, PFAS filter certifications didn't yet show removal all the way down to EPA's new limits. ⁠[20][21]
Reverse osmosis (RO)Parasites, bacteria and viruses. Also lead, copper, chromium, chloride and sodium. May also reduce arsenic, fluoride, radium, nitrate and sulfate. Units certified to NSF/ANSI 58 for PFAS reduce PFAS.Wastes about a gallon of water for every gallon it treats, and the cartridges and membrane need replacing. Check the label for the specific chemicals it removes.[22]
DistillationParasites, bacteria and viruses. Also many chemicals, including arsenic, barium, cadmium, chromium, lead, nitrate, sodium and sulfate.Some volatile organic compounds, volatile solvents and certain pesticides. Bacteria can grow on the cooling coils between uses. Distillers use more energy and take longer than other systems.[22]
Ultraviolet (UV) with pre-filtrationParasites, bacteria and viruses.Chemicals. Works poorly in cloudy water.[22]
Ion exchangeArsenic, copper and nitrate, according to CDC's treatment lists. Also PFAS (EPA) and radionuclides (EPA).Water softeners, which are a kind of ion exchange, do not remove parasites, bacteria or viruses.[23]

For emergency boiling and bleach steps, see Making water safe to drink.

03 What home tests can and cannot show

  • Start with your utility's water report. Every community water system has to send customers an annual water quality report (a Consumer Confidence Report) by July 1. If yours hasn't arrived, call the utility or look it up with EPA's search tool. ⁠[24]
  • The utility's lead testing covers the whole system, not your tap. It doesn't reflect conditions at your own faucet. Testing is the only way to know whether there is lead in your home's water. ⁠[25] You can't see, taste or smell lead dissolved in water. ⁠[26]
  • Store kits and strips can't replace a lab. Rhode Island's health department warns that kits bought in stores, or tests from companies that don't use a certified lab, "may not give you accurate results". ⁠[27] California's water board notes that a self-test kit only tells you whether something is present. A lab tells you how much is there. ⁠[28]
  • Taste and smell tell you nothing about safety. Harmful germs and chemicals often don't change how water looks, tastes or smells. ⁠[19]
  • Use a state-certified laboratory. EPA does not test home water on request. It keeps a list of each state's lab-certification program, and it encourages anyone who wants their water tested to contact a state-certified drinking water lab. ⁠[29] Your local health department may test private wells for free. ⁠[30]
  • PFAS samples are easy to contaminate. Ice packs, permanent markers and even some clothing can contain PFAS and spoil a sample. Follow the lab's instructions. ⁠[27]

04 Private wells

  • Test at least once a year for total coliform bacteria, nitrates, total dissolved solids and pH. Ask your health department what else to test for where you live. ⁠[2] EPA gives the same yearly list. ⁠[30]
  • Nobody else is watching your well. EPA's public-water rules don't apply to private wells, and the government does not regulate, treat or monitor well water. ⁠[2]
  • Test again if there is flooding, land disturbance or waste disposal near the well. Also test if you repair or replace any part of the well, if the taste, color or smell changes, if someone in the home becomes pregnant, or if a child comes to live with you. ⁠[2]
  • Before a baby arrives, test for nitrate early in the pregnancy, before bringing the baby home, and again during the baby's first six months. ⁠[25]
  • Radionuclides: EPA advises testing well water for them every three years. ⁠[31]
  • After a flood: don't drink from or wash with a flooded well, and stay away from the pump while it's flooded, because of the risk of electric shock. Have a well or pump contractor clean and disinfect the well before you turn the pump back on. Then pump it until the water runs clear. ⁠[30] Keep using another water source until the well has been checked and tested. ⁠[32]
  • Match the test to what's nearby. Near intensive farming, test for nitrate, nitrite, pesticides and coliform. Near gas drilling, test for chloride, sodium, barium and strontium. If your home has lead plumbing, test for pH, lead and copper. ⁠[30]
  • Use a state-certified lab. Your local health department may test for free, or can give you a list of certified labs. ⁠[30]

05 By region

Your region opens first once you choose your region.

Northeast / New England
  • Wells drilled into bedrock can contain naturally occurring arsenic and uranium. In Connecticut, the USGS projects that about 3.9% of private wells are above EPA's arsenic limit and 4.7% are above its uranium limit. ⁠[34]
  • A USGS/CDC study lists Maine, Massachusetts, New Hampshire and New Jersey among the areas with high arsenic in domestic wells. ⁠[36]
  • Uranium is concentrated in crystalline rock such as granite. Radon, a radioactive gas, comes from uranium as it decays. When radon-rich well water is used in the home, most of the radon escapes into the air, where breathing it raises lung cancer risk. ⁠[37]
  • Routine well tests usually leave out arsenic and uranium, so ask for them specifically. ⁠[34] EPA advises testing for radionuclides every three years. ⁠[31]
Local detail: Southeastern Connecticut
  • Connecticut requires testing only for new wells, under Section 19-13-B101 of the Public Health Code. After that, owners generally aren't required to test. Mortgage-related tests are required by the bank, not by law, and don't cover everything. ⁠[33]
  • The state health department recommends testing basic indicators every year. Test for arsenic, uranium and radon at least once, ideally every 5 years. Test for lead at least once, and again when planning a pregnancy or if a child under 6 lives in the home. Test for fluoride every 5 years when a child under 12 lives in the home. ⁠[33]
  • Any Connecticut well can have high arsenic or uranium, and routine tests usually leave them out. If a test shows uranium above 30 µg/L, treat the water. If arsenic is above the standard, use another water source or install treatment. ⁠[34]
  • Ledge Light Health District doesn't test well water itself, but it keeps a list of Connecticut-certified labs that do. ⁠[35]
Mid-Atlantic
  • Lead pipes are more likely in older cities and in homes built before 1986. Ask your utility whether your service line is lead. ⁠[26] Under the 2024 rule, utilities must replace lead service lines they control, most within 10 years. ⁠[38]
  • A USGS/CDC study lists New Jersey, Maryland and Virginia among the states with high arsenic in domestic wells. ⁠[36] Crystalline rock aquifers of the Piedmont, Blue Ridge, and Valley and Ridge are among the aquifers USGS flags for arsenic. ⁠[39]
  • In a 2000 USGS study of southeastern Pennsylvania, water from 46% of wells in the Chickies Quartzite exceeded EPA's radium limit. Radon in well water was also common. ⁠[40]
  • Along the Atlantic coast, heavy groundwater pumping can pull saltwater into freshwater aquifers. In extreme cases, supply wells have been abandoned. ⁠[41]
Southeast & Gulf Coast
  • Flooded wells are the main hazard. Don't drink the water, stay away from the pump while it's flooded, and have a contractor clean and disinfect the well before you use it. ⁠[30] Test after any nearby flooding. ⁠[2]
  • If fuel, heating oil or other chemicals may have reached the well, don't use it. Disinfecting won't fix that. ⁠[32]
  • Along the Atlantic coast, pumping near the shore can draw saltwater into wells. ⁠[41] Test for chloride, sodium and total dissolved solids if the water tastes salty. ⁠[30]
  • A USGS/CDC study lists Florida, North Carolina and South Carolina among the states with high arsenic in domestic wells. ⁠[36] USGS also flags aquifers in the Mississippi Embayment and the Mississippi River Valley for arsenic. ⁠[39]
Midwest / Great Lakes
  • USGS rates the Midwest at high risk for nitrate in shallow groundwater (less than 100 feet deep). Shallow wells are the most likely to exceed the nitrate limit. ⁠[42]
  • A USGS/CDC study lists Michigan, Wisconsin, Illinois, Ohio and Indiana among the states with high arsenic in domestic wells. ⁠[36]
  • If you are expecting a baby, test for nitrate early in the pregnancy, again before the baby comes home, and during the baby's first six months. ⁠[25]
  • Never boil water to get rid of nitrate. It concentrates it. ⁠[43]
Great Plains
  • In a USGS study of the central High Plains aquifer in south-central Kansas, 15% of the domestic wells sampled were above the nitrate limit. 80% showed nitrate above natural levels, likely from fertilizer, manure or livestock. ⁠[44]
  • Nitrate risk is highest where heavy nitrogen use, well-drained soils and little woodland come together. ⁠[42]
  • Near intensive farming, test for nitrate, nitrite, pesticides and coliform bacteria. ⁠[30]
  • Boiling makes nitrate worse. Nitrate is removed by ion exchange, distillation or reverse osmosis. ⁠[23]
Mountain West
  • In a USGS study of domestic wells in southwestern Montana, 14% were above EPA's uranium limit. Among wells drilled into granite of the Boulder batholith, 24% were above it. ⁠[45]
  • A USGS/CDC study lists Nevada and New Mexico among the western states with high arsenic in domestic wells. ⁠[36]
  • EPA advises testing well water for radionuclides every three years. It found ion exchange and reverse osmosis units at the tap work well for removing them. ⁠[31]
Desert Southwest
  • Arsenic is the biggest well-water concern. In USGS sampling, about 16% of Southwest drinking-water wells were above the arsenic limit, mostly from the volcanic and granitic rock the groundwater passes through. ⁠[39]
  • A USGS/CDC study lists Arizona, New Mexico and Nevada among the states with high arsenic in domestic wells. ⁠[36]
  • Natural fluoride can be high in this region. EPA's 2.0 mg/L secondary guideline was set as an upper limit for areas with a lot of naturally occurring fluoride, to protect children's teeth. ⁠[52]
  • Hard water leaves scale and makes it hard to lather soap. A water softener removes calcium and magnesium, but not germs. ⁠[22]
Local detail: Tucson, AZ
  • Tucson Water publishes its annual water quality report each June. ⁠[46] The 2025 report's highest results were arsenic 8.8 ppb, fluoride 0.80 ppm and nitrate 6.7 ppm. Each is below its legal limit, and none was a violation. ⁠[47]
  • PFAS: Tucson Water has taken almost 30 production wells out of service. It says wells with any PFAS detection are not serving customers, and it holds itself to stricter internal limits of under 2 ppt for PFOA and PFOS. ⁠[48] ADEQ says Tucson Water customers continue to receive water that meets all of EPA's PFAS limits, and that PFAS near Davis-Monthan Air Force Base threatens more wells. ⁠[49]
  • As of September 17, 2026, the city was considering a partnership with a nonprofit to speed up PFAS groundwater cleanup near Davis-Monthan. The city manager said the Air Force has "no near-term plan" to deal with it. ⁠[50]
  • Tucson's water is naturally hard, and it gets harder as more Colorado River water from the Central Arizona Project (CAP) is blended in. Hard water is safe to drink. ⁠[51]
  • If you have a private well in the Tucson area, test it for arsenic. Southwest basin-fill aquifers exceed the arsenic limit more than twice as often as wells nationwide. ⁠[39]
Pacific Northwest
  • Arsenic turns up in well water throughout Washington. Most water there has less than 3 ppb, but some wells have been found with anywhere from 10 ppb to 33,000 ppb. Test once in late summer and again in early spring. Washington has no statewide arsenic standard for private wells. ⁠[53]
  • In Oregon, anyone selling a property with a domestic well must have the water tested for arsenic, nitrate and coliform bacteria. ⁠[54]
  • A USGS/CDC study lists Washington and Oregon among the states with high arsenic in domestic wells. ⁠[36]
California
  • Nitrate in groundwater is a widespread problem, especially in the Tulare Lake Basin and the Salinas Valley. California writes its nitrate limit as 45 mg/L as nitrate, while EPA's is 10 mg/L as nitrogen, so check which units your lab report uses. ⁠[55]
  • In parts of the Central Valley, nitrate has built up in groundwater to the point that drinking water for rural households no longer meets safe standards. ⁠[56] The state has expanded a program that supplies free replacement water to nitrate-affected wells; it had covered more than 1,800 wells. ⁠[57]
  • If a domestic well serves a rental property inside a state-funded free testing program area, the owner must test the well through that program. ⁠[58]
  • California has its own limit for the cancer-causing solvent 1,2,3-TCP, in effect since December 14, 2017. Ask your lab about it if you are near farmland. ⁠[59]
  • The state recommends testing domestic wells every year. ⁠[28]
Alaska
  • Arsenic has been found in wells around Fairbanks, the Seward and Kenai Peninsulas, the Mat-Su Valley and Anchorage. It is likely in other places too. ⁠[60]
  • Alaska's health department recommends testing private wells for arsenic every year. Levels can change with the seasons or after an earthquake. ⁠[60]
  • Arsenic has no taste, smell or color, so only a test will find it. ⁠[60]
Hawaii
  • The health department does not regulate home rainwater catchment systems. Owners should design them well, maintain them regularly and test them from time to time. ⁠[61]
  • The health department screens catchment water for E. coli (there should be none), turbidity, lead (at or below 0.010 mg/L) and copper. Use a certified or approved lab, and take the sample at a tap after all treatment. ⁠[61]
  • Clean the roof, gutters, tank and filters regularly. Follow the University of Hawaii's Guidelines on Rainwater Catchment Systems for Hawaii. ⁠[61]
  • A certified filter removes only the contaminants listed on its certification. ⁠[61] CDC advises testing rainwater systems at least once a year. ⁠[19]

Sources

  1. National Primary Drinking Water Regulations · U.S. EPA · checked 2026-09-21
  2. Guidelines for Testing Well Water · CDC · checked 2026-09-21
  3. Chemical Contaminant Rules (arsenic) · U.S. EPA · checked 2026-09-21
  4. Lead and Copper Rule · U.S. EPA · checked 2026-09-21
  5. LCRI Questions and Answers · U.S. EPA · checked 2026-09-21
  6. EPA Defends 10-Year Lead Pipe Replacement Mandate (February 23, 2026) · Water Online · checked 2026-09-21
  7. American Water Works Association v. EPA (Lead and Copper Rule Improvements) · NRDC (intervenor defending the rule) · checked 2026-09-21
  8. EPA Releases New Guidance to Reduce Lead Exposure in Drinking Water (August 21, 2026) · U.S. EPA · checked 2026-09-21
  9. Revised Total Coliform Rule and Total Coliform Rule · U.S. EPA · checked 2026-09-21
  10. Fluoride in Drinking Water · U.S. EPA · checked 2026-09-21
  11. Proposed PFOA and PFOS Compliance Extension Rule · U.S. EPA · checked 2026-09-21
  12. From CERCLA to Drinking Water: D.C. Circuit's PFAS Ruling Enters a Second Regulatory Fight (September 3, 2026) · Pillsbury Winthrop Shaw Pittman (PFAS Observer) · checked 2026-09-21
  13. PFAS Litigation Information (court docket filings) · Association of Metropolitan Water Agencies (petitioner) · checked 2026-09-21
  14. Per- and Polyfluoroalkyl Substances (PFAS) - Final PFAS National Primary Drinking Water Regulation · U.S. EPA · checked 2026-09-21
  15. DC Court Denies EPA's Motion to Vacate Hazard Index PFAS from Drinking Water Rule (January 22, 2026) · Association of State Drinking Water Administrators · checked 2026-09-21
  16. Court Denies EPA's Motion to Sever and Stay Challenges to MCLs for Four Index PFAS (March 23, 2026) · Fox Rothschild (PFAS and Emerging Contaminants blog) · checked 2026-09-21
  17. Proposed PFAS Rescission Rule · U.S. EPA · checked 2026-09-21
  18. How to Make Water Safe in an Emergency · CDC · checked 2026-09-21
  19. About Choosing Home Water Filters · CDC · checked 2026-09-21
  20. Identifying Drinking Water Filters Certified to Reduce PFAS · U.S. EPA · checked 2026-09-21
  21. NSF Standards for Water Treatment Systems · NSF · checked 2026-09-21
  22. About Home Water Treatment Systems · CDC · checked 2026-09-21
  23. Chemicals That Can Contaminate Tap Water · CDC · checked 2026-09-21
  24. CCR Information for Consumers · U.S. EPA · checked 2026-09-21
  25. Home Water Testing (fact sheet) · U.S. EPA · checked 2026-09-21
  26. Basic Information about Lead in Drinking Water · U.S. EPA · checked 2026-09-21
  27. Testing Your Well Water · Rhode Island Department of Health · checked 2026-09-21
  28. GAMA - Domestic Well Testing · California State Water Resources Control Board · checked 2026-09-21
  29. Contact Information for Certification Programs and Certified Laboratories for Drinking Water · U.S. EPA · checked 2026-09-21
  30. Protect Your Home's Water (private wells) · U.S. EPA · checked 2026-09-21
  31. Natural Radionuclides in Private Wells · U.S. EPA (RadTown) · checked 2026-09-21
  32. Restoring and Testing Your Private Well After a Flood · New York State Department of Health · checked 2026-09-21
  33. Publication No. 24: Private Well Testing (May 2019) · Connecticut Department of Public Health · checked 2026-09-21
  34. Private Well Owners Urged to Test Water Quality: New USGS Report Shows High Arsenic/Uranium Levels in Some Wells · Connecticut Department of Public Health and USGS · checked 2026-09-21
  35. Wells · Ledge Light Health District · checked 2026-09-21
  36. Study Estimates about 2.1 Million People using Wells High in Arsenic · USGS and CDC · checked 2026-09-21
  37. Radionuclides (in groundwater) · USGS · checked 2026-09-21
  38. Lead and Copper Rule Improvements · U.S. EPA · checked 2026-09-21
  39. Arsenic and Drinking Water · USGS · checked 2026-09-21
  40. Fact Sheet 2000-0012: Naturally Occurring Radionuclides in the Ground Water of Southeastern Pennsylvania · USGS · checked 2026-09-21
  41. Freshwater-Saltwater Interactions along the Atlantic Coast (Saltwater Intrusion) · USGS · checked 2026-09-21
  42. A National Look at Nitrate Contamination of Ground Water · USGS (NAWQA) · checked 2026-09-21
  43. Frequently Asked Questions About Nitrate and Drinking Water (Lower Yakima Valley) · U.S. EPA · checked 2026-09-21
  44. Ground-water quality in Quaternary deposits of the central High Plains aquifer, south-central Kansas, 1999 · USGS · checked 2026-09-21
  45. Radiochemical constituents in groundwater of Jefferson County and surrounding areas, southwestern Montana, 2007-2010 · USGS · checked 2026-09-21
  46. 2025 Annual Water Quality Reports · City of Tucson, Tucson Water · checked 2026-09-21
  47. 2025 Annual Water Quality Report, Main System · City of Tucson, Tucson Water · checked 2026-09-21
  48. PFAS: Forever Chemicals · City of Tucson, Tucson Water · checked 2026-09-21
  49. Protecting Tucson's Drinking Water Supply (PFAS) · Arizona Department of Environmental Quality · checked 2026-09-21
  50. Tucson weighs partnership to speed PFAS groundwater cleanup (September 17, 2026) · KOLD News 13 · checked 2026-09-21
  51. Hard Water · City of Tucson, Tucson Water · checked 2026-09-21
  52. Secondary Drinking Water Standards - Guidance for Nuisance Chemicals · U.S. EPA · checked 2026-09-21
  53. Arsenic and Your Private Well · Washington State Department of Health · checked 2026-09-21
  54. Domestic Well Safety: Well Testing & Regulations · Oregon Health Authority · checked 2026-09-21
  55. Nitrate Project · California State Water Resources Control Board · checked 2026-09-21
  56. CV-SALTS (Central Valley Salinity Alternatives for Long-Term Sustainability) · CV-SALTS / Central Valley Salinity Coalition · checked 2026-09-21
  57. Central Valley Regional Water Quality Control Board · California Regional Water Quality Control Board, Central Valley · checked 2026-09-21
  58. Rental Property Domestic Well Testing Requirements (AB 2454) · California State Water Resources Control Board · checked 2026-09-21
  59. 1,2,3-Trichloropropane (1,2,3-TCP) · California State Water Resources Control Board · checked 2026-09-21
  60. Geologic Hazards: Arsenic in Groundwater · Alaska Division of Geological & Geophysical Surveys · checked 2026-09-21
  61. Rainwater Catchment · Hawaii Department of Health, Safe Drinking Water Branch · checked 2026-09-21