How to Test Water Quality at Home: Your Complete Guide

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The list of possible contaminants is extensive, many of which can exist naturally in various water sources. While not all of them are harmful, the ones that are can be very debilitating if consumed.

The effectiveness of water purification systems can vary greatly depending on the type of contaminant, which is precisely why testing is so important. You need to know what’s in the water before you can know how to treat it.

In this section, we’ll have a look at the different types of contaminants, what makes them dangerous, what levels are considered safe, and how to test for them.

The EPA categorizes contaminants according to their nature. These are physical contaminants, chemical contaminants, and biological contaminants.

Physical contaminants in water

Physical contaminants are more commonly found in groundwater and surface water sources, including sand, silt, and other large debris particles—they're mostly filtered at the source and typically don’t make it far enough through the water system.

These contaminants are generally visible to the naked eye and don’t require further testing unless testing for certain physical properties such as turbidity or TSS, which we’ll explore later.

Most physical contaminants follow the EPA’s secondary standards since they’re less likely to cause illness in humans and more likely to cause problems to the water system.

Biological contaminants in water

The biological contaminants category refers to living microorganisms in the water supply, including bacteria, viruses, and protozoa. Biological contaminants are commonly present in surface water sources such as lakes and rivers—likely due to fecal particles from animals.

Biological contaminants can also exist in shallow wells with a water table closely connected to a stream or in water distribution systems with poor sanitation practices. Developing regions with unregulated sanitation often experience many biological contaminants in the drinking water supply.

Biological contaminants are regulated according to the EPA's primary standards because of their high potential for causing severe illness in humans.

Bacteria: 0 ppm (0 mg/l)

Bacteria are single-celled organisms made up of a variety of different species. Some of the most common waterborne bacteria are e. Coli, Legionella, Salmonella, and Shigella.

Due to the wide variety of bacteria that can exist in water, testing for each species individually is impractical. Therefore, testing for widespread indicator bacteria such as coliforms is a more suitable approach.

Coliforms are a group of closely related bacteria that exist throughout the environment and are very easy to test for. While not necessarily harmful on their own, their presence in the water supply may also indicate the presence of other harmful bacteria. Testing for Total Coliforms may help identify if further testing for more dangerous bacteria is needed.

All bacteria should have a presence of 0 ppm (0 mg/l) according to the EPA's primary standards.

Viruses: 0 ppm (0 mg/l)

Viruses are the tiniest of waterborne pathogens, affecting the DNA structure of human and animal cells. Unlike bacteria, viruses require a host to reproduce.

Some of the most common waterborne viruses are Hepatitis, Norovirus, and Rotavirus. Contracting a waterborne virus can make one extremely ill, with symptoms of vomiting and diarrhea.

All viruses should have a presence of 0 ppm (0 mg/l) according to the EPA's primary standards.

Protozoa: 0 ppm (0 mg/l)

Protozoa are a group of microorganisms that are parasitic in nature, requiring a host to reproduce. Protozoa are larger in size than bacteria and viruses and often have protective membranes, making them more resistant to disinfection than other pathogens.

Like bacteria and viruses, protozoa are typically found in surface water sources where animal feces may be present.

All protozoa should have a presence of 0 ppm (0 mg/l) according to the EPA's primary standards.

Chemical contaminants in water

The chemical category of contaminants is certainly the most diverse group of contaminants on this list, ranging from naturally occurring elements to man-made chemicals.

Because such a wide variety of chemical contaminants can exist in the water supply, both naturally and synthetically, a first-level testing method should be applied first to get a general idea of the presence of potential contaminants.

A home testing kit would be a great way to get a general idea of the structure of the water. The chemicals that are present can be further tested at a laboratory to get exact levels and, thus, better treatment options.

Organic vs Inorganic

Chemical contaminants are classified as either organic or inorganic. While these terms may seem to refer to whether a contaminant exists naturally or is man-made, they actually refer to its chemical makeup.

Inorganic compounds refer to any chemical that lacks the carbon element, while organic compounds include the carbon element.

Inorganic Chemical Compounds

Inorganic compounds often come from rock formations within the earth’s crust and are more common in groundwater than in surface water sources. Some inorganic compounds, such as calcium and magnesium, are beneficial for human consumption at low doses; others, such as arsenic, are highly toxic.

Problematic Elements:

Iron: < 0.3 ppm (0.3 mg/l)
Manganese: < 0.05 ppm (0.05 mg/l)

Like the minerals that cause water hardness, these problem elements are common in groundwater sources and are more of an aesthetic nuisance than a health concern.

Iron and Manganese can cause discoloration in the water and piping system.

Heavy Metals:

Arsenic: 0 ppm (0 mg/l)
Cadmium: < 0.005 ppm (0.005 mg/l)
Copper: < 1.3 ppm (1.3 mg/l)
Lead: 0 ppm (0 mg/l)
Mercury: < 0.002 ppm (0.002 mg/l)

Heavy metals can cause numerous health problems in individuals if consumed. These health problems include neurological, digestive, liver disease, and cancer.

Heavy metals can either exist naturally in the water supply, enter the water supply through industrial contamination, or be leached into the water supply via corroding pipes.

Fluoride: < 2 ppm (2 mg/l)

While fluoride can be found naturally in groundwater and surface water sources, some municipalities add fluoride to the public water supply as a dental benefit. Small amounts of fluoride have been proven to have some benefits in strengthening teeth, but too much fluoride can cause some serious health issues.

Nitrates: < 10 ppm (10 mg/l)
Nitrites: < 1 ppm (1 mg/l)

Nitrogen exists naturally in soil and is an active ingredient in gardening fertilizer. Bacteria in the soil convert Nitrogen into Nitrates/Nitrites, a consumable form for plants.

Excess nitrates/nitrites in the soil can leach into the water supply, causing health problems for humans.

Organic Chemical Compounds

While the term “organic” may seem to indicate a naturally occurring substance, it merely refers to the presence of the carbon element. Ironically, many substances that include the carbon element are actually man-made—existing as pesticides, industrial byproducts, and pharmaceutical drugs.

Because of its close relation to industrial and agricultural byproducts, often resulting in the pollution of water sources, organic compounds are often found in surface water sources in close proximity to potential contamination sites. Some organic compounds can even be found in municipal water sources.

Some organic compounds can pose a serious health risk if consumed, often resulting in neurological or gastrointestinal disorders or even cancer.

Organic compounds are further divided into two groups: VOCs and SOCs.

VOCs

Benzene: < 0.005 ppm (0.005 mg/l)
Carbon tetrachloride: < 0 ppm (0 mg/l)

VOCs, volatile organic compounds, are compounds that vaporize easily into the atmosphere. These include industrial chemicals such as benzene and carbon tetrachloride.

SOCs

Glyphosate: < 0.7 ppm (0.7 mg/l)
Atrazine: < 0.003 ppm (0.003 mg/l)

SOCs, synthetic organic compounds, are less likely to vaporize into the air. These include agricultural herbicides and pesticides such as Glyphosate and Atrazine.

PFAS (Per- and Polyfluoroalkyl Substances)

EPA MCL: 4 ppt (PFOA and PFOS as of April 2024)

PFAS — per- and polyfluoroalkyl substances — are a class of over 12,000 synthetic chemicals used since the 1940s in non-stick cookware, stain-resistant fabrics, food packaging, and firefighting foam. Because their carbon-fluorine bonds don't break down naturally, they persist in soil, groundwater, and the body indefinitely — which is why they're commonly called forever chemicals.

The EPA estimates that PFAS are detectable in the drinking water of approximately 45% of U.S. public water supplies. Exposure is linked to kidney cancer, testicular cancer, thyroid disease, immune suppression, and reproductive issues (EPA PFAS Health Effects).

In April 2024, the EPA established the first-ever federal MCLs for PFAS: 4 parts per trillion (ppt) for PFOA and PFOS individually, and combined limits for four additional PFAS compounds. Public water utilities are required to test and treat accordingly by 2027. For current coverage of the rule and its regulatory status, see The EPA Set Limits on Forever Chemicals. Now It's Dismantling Them.

Who should test: Test if you live near a military base, airport, or industrial facility that used AFFF firefighting foam; near a manufacturing plant that makes fluorinated products; or in any area flagged by the EWG PFAS Contamination Map as having known groundwater contamination. Private well owners are not covered by the 2024 rule and should test independently.

How to test for PFAS: Standard test strips and TDS meters do not detect PFAS. You need a certified laboratory using EPA Method 537.1 or Method 533, which can measure PFAS at the parts-per-trillion level. Labs that offer PFAS panels include Tap Score, National Testing Laboratories, and state-certified labs through your health department. Expect to pay $100–$300 for a comprehensive PFAS panel.

If your test comes back above 4 ppt: Reverse osmosis removes PFAS effectively — NSF/ANSI 58 certified RO systems are among the most reliable point-of-use treatment options (NSF). Granular activated carbon (GAC) also reduces PFAS levels, though less consistently across all compound types. Whole-house treatment is available but costly; most households prioritize point-of-use RO at the kitchen tap for drinking and cooking water.

Other Water Properties

Hardness

We’ve addressed the basics of hardness earlier when mentioning the beneficial inorganic compounds of calcium, magnesium, and potassium. While these elements aren’t necessarily harmful to consume—and can, in fact, have health benefits in small amounts— excess concentrations of these minerals can cause water hardness.

Water hardness is the over-concentration of minerals that can cause build-up within water pipes and calcium deposits on faucets, showerheads, and other fixtures.

Water hardness can also reduce the efficiency of soap lathering and can cause irritation to sensitive skin and hair.

While not a health concern, hardness is more of an aesthetic and functional problem that can require expensive repairs if left untreated.

pH

pH measures how acidic or basic the water is on a scale of 0-14. A pH of 7 is considered neutral. Anything higher than a seven is considered basic while anything lower is considered acidic.

Measuring the pH of the water is useful for many applications, including gardening, aquarium care, hydroponics, and aquaponics.

pH can also be a factor in water hardness and iron treatment. A pH of greater than 8.5 can indicate a hardness problem as it can mean a higher concentration of calcium and magnesium.

A higher pH level can also make the treatment for iron oxidation much easier as iron turns ferric at pH levels greater than 7.0.

Lower pH levels can cause corrosion of water pipes and leach heavy metals into the water supply.

Testing for pH can be done easily with home test strips.

The EPA sets a standard range for pH levels at 6.5 to 8.5.

TDS / Electroconductivity

TDS, or Total Dissolved Solids, refers to the total amount of dissolved inorganic minerals that are within the water. Dissolved solids cannot be seen with the naked eye as they’ve been broken down into their simplest chemical form.

TDS generally consists of inorganic salts, including calcium, magnesium, potassium, sodium, bicarbonates, chlorides, and sulfates, and oftentimes small amounts of organic matter.

An example of TDS can be seen when comparing ocean water with spring water. Ocean water has a very high level of TDS, evidenced by the high concentration of salt. Spring water has a lower level of TDS as it generally consists of moderate levels of calcium, magnesium, and other minerals.

Measuring TDS is a great way to get an idea of the structure of the water as it informs you of how much “stuff” is in there. While TDS measurements don’t necessarily tell you the exact measurement of each chemical, high concentrations of TDS can indicate the need for further, more extensive testing.

TDS is measured by a TDS meter that tests the electroconductivity of the water. Water itself isn’t electroconductive, but the minerals within the water allow it to conduct electricity. A higher level of dissolved solids within the water will give a higher electroconductivity reading.

TSS / Turbidity

Where TDS measures the Total Dissolved Solids within the water, TSS measures the Total Suspended Solids within the water.

Suspended solids generally refer to a collection of larger particles that haven’t dissolved into the water, such as sand, silt, and larger chemical compounds.

Turbidity refers to the clarity of the water in the presence of these suspended solids. Water with high turbidity will appear very cloudy and murky, while water with low turbidity appears clear.

Measuring turbidity is important because high turbidity can often indicate the presence of harmful pathogens. Bacteria, viruses, and protozoa are able to find refuge in large particles such as sand and silt, making it harder to disinfect.

UV purification devices often require a sediment filter to reduce turbidity before applying ultraviolet radiation. Large particles of sand can often block the UV light from killing pathogens, rendering it less effective.