Interpreting Your Water Test Reports

Select a topic from the following list for more information:

Also available is some information on irrigation water quality.  Much of the following information is also available in a full color printable pdf format file (0.8 MB).


The following information was taken from an NDSU Extension Service Report, Interpreting Your Water Test Report, November 1987.

Alkalinity: Alkalinity is a measure of the capacity of water to neutralize acids. The predominant chemical system present in natural waters is one where carbonates, bicarbonates and hydroxides are present. The bicarbonate ion is usually prevalent. However, the ratio of these ions is a function of pH, mineral composition, temperature and ionic strength. A water may have a low alkalinity rating but a relatively high pH or vice versa, so alkalinity alone is not of major importance as a measure of water quality. Alkalinity is not considered detrimental to humans but is generally associated with high pH values, hardness and excess dissolved solids. High alkalinity waters may also have a distinctly flat, unpleasant taste.

Calcium and Magnesium: Calcium and Magnesium are important contributors to water hardness. When water is heated they break down and precipitate out of solution, forming scale. Maximum limits have not been established for these parameters. Magnesium concentrations greater than 125 mg/L may have a laxative effect on some people.

Chloride: High concentrations of chloride ions may result in an objectionable salty taste to water and the corrosion of plumbing in the hot water system. High chloride waters may also produce a laxative effect. An upper limit of 250 mg/L has been set for the chloride ions, although at this limit few people will notice the taste. Higher concentrations do not appear to cause adverse health effects. An increase in the normal chloride content of your water may indicate possible pollution from human sewage, animal manure or industrial wastes.

Conductivity: Conductivity is the measure of the conductance of the water to an electric current. Conductivity is commonly reported as umhos/cm (micromhos per centimeter). This is an easy measurement to make and relates closely to the total dissolved solids content of the water. The total dissolved solids is approximately 70 percent of the conductivity in umhos/cm.

Fluoride: At concentrations greater than 1.0 mg/L, fluoride will reduce the incidence of dental cavities. At concentrations greater than 1.5 mg/L, fluorosis (mottling) of teeth may occur. Most municipal water supplies have added fluoride to reach the optimal level of 1.2 mg/L to reduce cavities. Some water supplies in North Dakota contain naturally occurring fluoride in amounts high enough to cause mottling of the teeth.

Iron and Manganese: Iron in concentrations greater than 0.3 mg/L and manganese in concentrations greater than 0.05 mg/L may cause brown and black stains on laundry, plumbing fixtures and sinks. A metallic taste may also be present and it may affect the taste of beverages made from the water. High concentrations of iron and manganese do not appear to present a health hazard.

Nitrate: Nitrate levels should not be higher than 10 mg/L if reported as nitrogen (N). High nitrate may cause methemoglobinemia (infant cyanosis or "blue baby disease") in infants who drink water or formula made from water containing nitrate levels higher than recommended. Adults can drink water with considerably higher concentrations than infants without adverse affects. Livestock water can contain up to 100 mg/L of nitrate as nitrogen, but young monogastric animals such as hogs may be affected at nitrate levels considerably less than 100 mg/L.

pH: pH is a measure of the hydrogen ion concentration of the water. The pH of water indicates whether the water is acid or alkaline. The measurement of pH ranges from 1 to 14 with a pH of 7 indicating a neutral solution, neither acid nor alkaline. Numbers lower than 7 indicate acidity; numbers higher than 7 indicate alkalinity. Drinking water with a pH of between 6.5 and 8.5 is generally considered satisfactory. Acid waters tend to be corrosive to plumbing and faucets, particularly if the pH is below 6. Alkaline waters are less corrosive. Waters with a pH of above 8.5 may tend to have a bitter or soda like taste. The pH of water may have an effect on the treatment of water and also should be considered if the water is used for field application of pesticides. Water with a pH of 7.0 to 8.5 will require more chlorine for the destruction of pathogens than will water that is slightly acidic.

Potassium: Potassium concentrations in water are generally very small. Although excessive intakes may have a laxative effect, public health authorities have not established a maximum limit.

Sodium: Sodium is a very active metal which does not occur in nature in a free state. It is always combined with other substances. In the human body sodium helps maintain water balance. Human intake of sodium is mainly influenced by the consumption of sodium as sodium chloride or table salt. The contribution of drinking water is normally small compared to other sources. The treatment for certain heart conditions, circulatory or kidney diseases or cirrhosis of the liver may include sodium restriction. Diets for these persons should be designed with the sodium content of their drinking water taken into account. The National Academy of Sciences has suggested a standard for public water allowing no more than 100 mg/L of sodium. This would insure that the water supply adds no more than 10 percent of the average person's total sodium intake. The American Health Association has recommended a more conservative standard of 20 mg/L to protect heart and kidney patients.

High concentrations of sodium will reduce the suitability of water for irrigation or house plant watering use. High sodium water will alter the soil chemistry and absorption properties, eventually sealing the soil surface.

Softening water by ion exchange or lime-soda ash processes will increase the sodium content. Softening by ion exchange will increase the sodium content by approximately 8 mg/L for each grain per gallon of hardness removed.

Sulfate: Water containing high levels of sulfates, particularly magnesium sulfate (Epsom salts) and sodium sulfate (Glauber's salt) may have a laxative effect on persons unaccustomed to the water. These effects vary with the person and appear to last only until one becomes accustomed to using the water. High sulfate content also affects the taste of water and will form a hard scale in boilers and heat exchangers. For these reasons the upper recommended limit for sulfates is 250 mg/L.

Total Dissolved Solids: High concentrations of total dissolved solids (TDS) may cause adverse taste effects. Highly mineralized water may also deteriorate domestic plumbing and appliances. It is recommended that waters containing more than 500 mg/L of dissolved solids not be used if other less mineralized supplies are available. This does not mean water containing more than 500 mg/L TDS is unusable. Exclusive of most treated public water supplies, the Missouri River, a few fresh lakes and scattered wells, very few water supplies in North Dakota contain less than 500 mg/L concentration of total dissolved solids. Many households in the state use drinking water supplies with concentrations of 2000 mg/L and greater.

Total Hardness: Hardness is the property which makes water form an insoluble curd with soap and is primarily due to the presence of Calcium and Magnesium. Waters which are very hard have no known adverse health effects and may be more palatable than soft waters. Hard water is primarily of concern because it requires more soap for effective cleaning, forms scum and curd, causes yellowing of fabrics, toughens vegetables cooked in the water and forms scale in boilers, water heaters, pipes and cooking utensils.

The hardness of good quality water should not exceed 270 mg/L (15.5 grains per gallon) measured as calcium carbonate. Water softer than 30-50 mg/L may be corrosive to piping depending on pH, alkalinity and dissolved oxygen.

Turbidity: Turbidity is a measure of light transmission and indicates the presence of suspended material such as clay, silt, finely divided organic material, plankton and other inorganic material. Turbidities in excess of 5 are usually objectionable for aesthetic reasons. If turbidity is high, be aware of possible bacterial contamination.


Irrigation Water Quality

The following image was taken from the California State Water Resources Control Board, Water Quality Criteria Manual
Irrigation Classification Chart
Retrieve the same image at a larger size, making it easier to read.


Irrigation water must be considered from the standpoint of the total salts (salinity) it contains and the amount of sodium (alkalinity) it carries. Both factors will prove harmful if they are allowed to accumulate in the soil. The sodium is usually the more serious problem.

In North Dakota many groundwater sources are unacceptable for irrigation. The suitability of water for irrigation depends both upon the water itself and upon the soil it is to be used on. A sandy soil can take a poorer quality water than a clay soil because the water carries away the salts and sodium as it drains.

The County Extension Agent has a knowledge of the soil conditions in your area, and should be consulted for more specific information concerning irrigation waters.

The salinity hazard of irrigation water is measured as electrical conductivity in terms of micromhos/cm at 25 degrees C.

C-1 (0-250 micromhos): Low salinity water can be used for irrigation with little likelihood that soil salinity will develop.

C-2 (250-750 micromhos): Medium salinity water can be used for irrigation if a moderate amount of leaching occurs.

C-3 (750-2250 micromhos): High salinity water should be used only on soils of moderate to good permeability. Leaching is needed to prevent serious soil salinity.

C-4 (above 2250 micromhos): Very high salinity water is generally undesirable for irrigation and should be used only occasionally on soils of good or high permeability where special leaching is provided to remove excess salt.

The sodium hazard of irrigation water is dependent on the Sodium Adsorption Ratio (SAR) and the electrical conductivity of the water.

S-1: Low sodium water can be used on almost all soils with little danger of accumulating harmful amounts of exchangeable sodium.

S-2: Medium sodium water can be used on coarse textured soils with good permeability but is dangerous when used on fine textured soils.

S-3: High sodium water tends to cause harmful sodium accumulations and requires special soil management, good drainage, high leaching, and organic matter additions.

S-4: Very high sodium water is generally unsatisfactory for irrigation purposes.