Soil and Plant Testing Laboratory
573-882-0623
Interpretation guide for domestic water analysis
Water analysis measures substances dissolved in water. Water is a very effective solute. Therefore, in nature it never occurs in a pure form, but rather it always contains "contaminants." These contaminants result in water characteristics such as hardness, electrical conductivity, corrosiveness, etc. Some of the substances in water pose a health risk when present in sufficient quantities, while others result in unaesthetic or nuisance conditions. Of the contaminants tested for by the MU Soil and Plant Testing Laboratory, only nitrate poses a health threat.
Water analysis results are compared to Secondary Maximum Contaminant Levels (nitrate excepted) Water that meets these standards should result in no unpleasant taste, appearance, odor or other side effects. For nitrate the Maximum Contaminant Level is that at which no deleterious health effects are anticipated.
The following list describes different water analyses and their relevance to domestic use.
- pH
A general water quality indicator, pH indicates whether water is acid or alkaline. The type of substances dissolved in water affects its pH. Acid water with a pH less than 6.0 will be corrosive to plumbing and facets, resulting in pitting or deposits. Low pH also tends to make metals and hardness minerals more soluble, which can dissolve metals from pipes and result in an unusual taste Water with a pH greater than 8.5 will have a bitter soda like taste.
- Total dissolved solids
This is a measure of all the inorganic substances dissolved in water, which includes minerals and salts. High values indicate an excess of some specific substance. Depending on the substance in excess, this can result in hard water, an objectionable taste (salty or bitter) or possibly a harmful health effect. Total dissolved solids is usually closely related to total dissolved salts and electrical conductivity.
- Electrical conductivity
Pure water is a poor conductor of electricity. As the concentration of dissolved salts (usually salts of sodium, calcium and magnesium, bicarbonate, chloride, and sulfate) increases in water, electrical conductivity increases. Electrical conductivity relates to the salinity of water.
- Hardness
Hard water is caused by calcium and magnesium dissolved in water. It is a relative term as shown in the table below. Hardness minerals react with soaps making them difficult to lather or causes them to form a scum, which is deposited on wash fixtures or clothes. These minerals in heated water will also precipitate as scale in appliances, pots, water heaters or pipes. Hard water has no known deleterious health effect.
- Bicarbonates
Bicarbonate is a negatively charged ion that associates with calcium and magnesium to form salt, which under the right conditions can precipitate from water as scale in pots and on pipes and fixtures. Bicarbonate can be a major contributor to water alkalinity.
- Sodium
Sodium is a metal that usually exists in water as a positively charged
ion -- half of sodium chloride (table salt). There exists no national standard
contaminant level for sodium, because the body readily excretes excess sodium.
However, a maximum level of 20 ppm is recommended for people on low sodium diets.
Water softening usually increases water sodium levels by about 8 ppm.
- Chloride
High chloride concentrations in water result in an objectionable salty taste and can cause corrosion of plumbing in hot water systems.
- Nitrate
Nitrate in water interfers with the body's capacity to absorb oxygen. High nitrate levels in water adversely affect infants and pregnant women. Infants are particularly susceptible-the condition is methemoglobinemia (infant cyanosis or blue baby disease). Adults are tolerant to much higher levels. The nitrate standard is established to protect infants less than one year old.
- Sulfate. Large amounts of sulfate in water can result in
- A bitter or medicinal taste
- The formation of scale in boilers and
heat exchangers
- A laxative effect. The laxative effect is unlikely
to occur at levels less than 500 ppm.
- Iron. High iron concentrations can impart an objectionable metallic taste or odor to water and cause a red or brown staining of laundry and porcelain fixtures. High concentrations do not pose a health hazard.
- Manganese. High manganese concentrations can impart a bitter taste to water and cause black or gray stains to laundry and porcelain fixtures. These stains can be more difficult to remove than iron stains. High concentrations do not pose a health hazard.
- Copper. Copper concentrations exceeding 1 ppm impart a bitter, metallic taste to water and at concentrations greater than 2 ppm may cause a blue-green staining of plumbing fixtures. Copper in water is not a health concern.
- Calcium and Magnesium. These minerals are responsible for water hardness.
- Potassium. Potassium has the same effect as sodium in water.
Updated
4/26/05
