Analytical Chemistry Laboratory:
Water Quality Evaluation

What do the results of my water analysis mean?

All groundwaters contain various kinds and amounts of dissolved salts (sometimes called minerals). These salts originate from small amounts dissolved in rainwater from particles in the air and from the dissolution of soils and rocks as water moves through the ground. Small quantities of many salts are essential to good health and improve the taste of the water. Excessive amounts of some can be a nuisance, be corrosive to plumbing or even hazardous to health.

When a well is drilled, a water analysis is generally carried out to determine if the dissolved salts exceed guideline or standard values. The term "potable" water refers to water that meets the U.S. Environmental Protection Agency (USEPA) standards for drinking water and includes physical, biological, inorganic, organic, and radiological parameters. However, unless there is a specific reason for believing well water to be contaminated, an analysis of the inorganic parameters (dissolved salts) is sufficient.

Compare your well analysis to these limits. USEPA drinking water limits are shown as well as the NM standards for groundwater that is to be used for drinking water. Irrigation and livestock water are other uses that are listed. USEPA limits apply only to public drinking water supplies (a source that supplies 15 or more connections) and are listed here for comparison. A complete list of USEPA maximum contaminate levels (MCLs) may be found at http://www.epa.gov/safewater/mcl.html#mcls

Nitrate

Nitrate almost never occurs in groundwater naturally and can result from over fertilization, unlined evaporation ponds at dairies, septic tanks, and some milling operations. If the water contains a value higher than 5 ppm nitrate as (NO₃) then an analysis for bacterial contamination is recommended.

Hardness

Hardness is a measure of the amount of calcium and magnesium in the water. Hard waters can cause the build up of scale in hot water pipes, fittings, and in your hot water heater. They also require more soap to obtain suds. Many New Mexico groundwaters are hard and some are very hard. The hardness can be removed by softening the water before it enters the hot water heater. This process replaces the calcium and magnesium with sodium or potassium depending on whether sodium chloride or potassium chloride is used to regenerate the resin in the water softener. In the exchange process, one calcium or one magnesium ion is replaced by two sodium or potassium ions. So the total number of ions increases and if the water is too hard it becomes very salty. Anyone on a low sodium diet should not drink water softened with sodium salt.

Fluoride

Small amounts of fluoride are beneficial for teeth and help prevent decay. However, excess fluoride can cause the teeth to become stained and mottled. High amounts of fluoride occur in some groundwaters in New Mexico.

Total Dissolved Solids (TDS)

The USEPA permissible amount of dissolved salts in drinking water is 500 mg/L. Higher TDS are objectionable because of physiological effects, mineral taste, and corrosion in municipal water systems. In New Mexico, however, many private wells contain TDS higher than 500 mg/L and the NM Groundwater Standards contain a limit of 1000 mg/L.