How to Interpret Drinking Water Analysis Reports

By Engaged Expert John Rigdon

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Total coliform bacteria, nitrate, pH, hardness and total dissolved solids all affect water quality and are reported in a drinking water test report.

Though other contaminants can be analyzed, testing for them can often be expensive and unnecessary. It is more important to test drinking water on a regular basis for a few indicators of contamination and to maintain good records.

An explanation of the terms often appearing on drinking water analysis reports are shown in this Fact Sheet. Tables showing the EPA Maximum Contaminant Levels (MCL) and Secondary Drinking Water Regulations (SDWR) for some of the analytes are on the back of this sheet. MCLs are the highest level of a contaminant allowed in drinking water. SDWRs are non-enforceable Federal guidelines regarding cosmetic or aesthetic effects.

Total Coliform

This is a bacteriological analysis which indicates if a drinking water supply has been contaminated with human or animal waste. If the result of this test is positive, the water should not be used for human consumption unless it is boiled for five minutes or disinfected by other means.


A pH of less than 6.5 can cause health problems. Municipal water supplies are usually adjusted to values between 8.0 and 10.0. Highly acidic water can be corrosive and may dissolve metals from pipes, pumps, and other fixtures. SDWR standards suggest a pH range between 6.5 to 8.5 for drinking water.


Water containing excessive levels of calcium and magnesium is said to be “hard”. Hard water does not affect health but can cause scaly deposits to form in pipes and water tanks. It is desirable that water tests below 150 mg/l hardness and not higher than 500 mg/l.

Hardness Ratings* mg/l Grains/Gallon
Soft less than 2.9
Moderately Soft 50 to 100 2.9 to 8.8
Hard 150 to 300 8.8 to 17.5
Very hard >300 >17.5
*Handbook of Drinking Water Quality (Van Nostrand Reinhold Publishing, 1900)

It is desirable that water tests below 150mg/l hardness and not higher than 500 mg/l.

Electrical conductivity (EC) and total dissolved solids

Electrical conductivity (EC) measures the soluble salt concentration in mmhos/cm and is used to calculate the total dissolved solids (TDS) in water supplies. The EC should not exceed 0.78. Water containing more than 500 mg/l total dissolved solids is not recommended for human consumption.

Nitrate (N)

A high concentration of nitrate can be fatal to infants and a threat to young farm animals. High levels may occur near manure piles, fertilized fields or subdivisions using septic tanks. Levels should not exceed 10 mg/l Nitrate (N) or 1 mg/l Nitrite (as N). 

Maximum Contaminant Levels
 Arsenic (As) 10 ug/l
 Flouride (F) 4 mg/l
Cadmium (Cd) 5 ug/l
Lead (Pb) 15 ug/l
Copper (Cu) 1300 ug/l
Mercury (Hg) 2 ug/l


Secondary Drinking Water Regulation Levels
Chloride (Cl) 250 mg/l
Sulfate (SO4) 250 mg/l
Iron (Fe)** 0.30 mg/l
Zinc (Zn) 5 mg/l
Manganese (Mn)** 0.05 mg/l
**Iron and Manganese are often present together.  They may cause rusty water, stains, deposits, and affect water's taste, but they are not a health hazard
Water Treatment Methods 

Absorption Filter

    Reduces poor taste, bad odor, turbidity, chloride, radon, organic contaminants, iron and arsenic. 
Reverse Osmosis     Reduces dissolved inorganic and some organic contaminants. Reduces various cations (i.e. lead, chromium and cadmium).
Ion Exchange     Reduces calcium, magnesium, barium, nitrate, fluoride and other mineral levels
Distillation     Removes all but volatile contaminants. Inactivates or removes pathogens.

Water Softener

    Reduces hardness and may remove manganese and small amounts of iron.
Chlorination     Removes iron, manganese and any iron or manganese related bacteria. It is more effective in Removing iron in dissolved or precipitated forms if it is followed by filtration.
Drinking Water Sample Collection

Drinking Suitability

Locate a sampling point near the well, before the water sampler. Turn on the water and allow it to run long enough to flush the system out with water. If a coliform test is required, turn off the water and pass a flame back and forth over the outlet to sterilize. Turn on the water at a moderate flow rate. Carefully fill a sterile container and reattach the lid. If other drinking suitability tests are required, fill a second container from the running faucet and seal the lid. Samples should be refrigerated after collection and transported to the lab within 24 hours.

Lead and Copper

Sample at the kitchen faucet or from wherever most drinking water is taken. The sample should be collected the first thing in the morning, before anyone has drawn water. Fill a 1-pint container directly from the faucet without allowing the water to run first. If any of the above tests are being run, a separate sample should be taken for lead and/or copper.

Abbreviations, Conversions and Equivalents
> more than No3-N NO3 x 0.226
less than SO4 -@ SO4 x 0.333
mg/l milligrams per liter TNTC too numerous to count
mmho/cm unit of conductance 17.1 mg/l 1.0 grain/gallon
ug/l micrograms per liter EC electrical conductance

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