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This guide summarizes information to help interpret the basic laboratory results for a sample representing a household or domestic water supply. All natural waters contain minerals or other substances that may have dissolved from the sand or rocks that were in contact by the water over time. A water supply can be contaminated by minerals or microorganisms introduced from the outside through direct entry into the water supply from defects or damage to the well or plumbing. A ServiTech laboratory analysis can help identify the suitability of a water supply or water source for drinking, household and domestic use.
Milligram per liter (mg/L) is way of expressing chemical concentrations in liquids. “mg/L” is equivalent to “parts per million (ppm)”. “Microgram per liter (μg/L)” is equivalent to “parts per billion (ppb)”.
Maximum contaminant level (MCL) is a standard established by the US-EPA for several water constituents. A water supply that exceeds the MCL is considered a potential hazard to human health. Such a supply should not be directly consumed. That is, do not use for drinking or food preparation. It may be acceptable for washing clothes or bathing, however.
Secondary maximum contaminant level (SMCL) is a standard related to water appearance, taste, or smell. A water supply exceeding the SMCL is not considered to pose a hazard to human health, but may not be desirable for domestic use if it cannot be treated to a level below the SMCL.
Coliform bacteria refers to a family of bacteria widely found in the environment, in soil and on plants, but also in feces of warm-blooded animals. It is a relatively simple, standard test for microbiological safety. Coliform bacteria are not considered pathogens, but a positive test suggests the water supply has been exposed to the environment. Other disease organisms, like Giardia, Cryptosporidium, or viruses may have also entered the water supply, so disinfection of the water supply is recommended.
E. coli refers to “fecal” coliforms. A positive test suggests recent entry of contamination from a source of animal or human waste.
Electrical conductivity (EC) is a measure of the ability of a water sample to conduct an electric current. Conductivity is an easy measurement to make. It is closely related to the total dissolved solids (dissolved mineral) content of the water source.
Total dissolved solids (TDS) are found at some level in all natural, untreated waters. TDS may contribute to mineral nutrition, but can be a nuisance or harmful at excessive levels. Problems include scale formation, corrosion, and reduced life of water heaters or other plumbing appliances.
Nitrate (NO3) is very common in the environment. Few natural waters are completely free of nitrate. Concentrations may be expressed as either nitrate-nitrogen (NO3-N) or nitrate (NO3), differing by a factor of 4.43. Common sources of nitrate are soil, animal waste, septic systems, fertilizer, and/or organic wastes.
Fluoride (F) can help protect against dental cavities, but high levels may cause discoloration (mottling) of the teeth. Excessive levels may cause skeletal damage and bone disease. Most municipalities add supplemental fluoride to their water supplies because natural levels are often low.
Sulfate (SO4) is a common water component because it is easily dissolved from soil and rock. High sulfate levels may impart a disagreeable taste to water and may have a laxative effect on people unaccustomed to drinking the water. Scale may form in water heaters from high sulfate levels. Sulfate-reducing bacteria may become a problem in certain situations requiring disinfection and/or treatment.
Chloride (Cl) at excessive levels increases water corrosiveness of water. It may give water a salty taste when combined with excess sodium. Excess chloride may accelerate corrosion of metal plumbing fixtures.
Calcium (Ca) and magnesium (Mg) minerals are primary contributors to water hardness. These two components precipitate out of solution when water is heated. This may form scale deposits on insides of plumbing fixtures and appliances.
Sodium (Na) is common in natural waters, but typically at low levels. Sodium chloride is commonly used for water softening, so soft water usually has elevated sodium levels. Drinking water sodium can contribute to dietary sodium, so is of concern to those with restricted sodium diets.
Iron (Fe) concentrations are usually very low in drinking water. Excess iron may leave brownish deposits on laundry, plumbing fixtures, and sinks. The presence of iron reducing bacteria may contribute to the problem, requiring disinfection and/or treatment. Drinking water may have a metallic taste if iron levels are high, but there is no health hazard.
Manganese (Mn) in drinking water has no known health effects. It may be associated with high iron. Excess manganese may cause black or gray color in laundry and dark stains on plumbing fixtures and sinks.
Hardness minerals do give flavor to drinking water and have no known adverse health effect. Excessive hardness forms scale in plumbing and appliances, so contributes to early failure. Hardness minerals react with detergents to produce soap scum leaving unsightly bathtub rings and deposits on clothes. Softening reduces calcium and magnesium concentrations, but may encourage pitting of copper pipe in certain situations.
¶ Table 1. Household (Domestic) Water Quality Ratings |
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| Analysis Result | ------------------- General Category ------------------- | Secondary Maximum Contaminant Level (SMCL) |
Maximum Contaminant Level (MCL) |
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| Low | Moderate | High | Very High | Extremely High | Excessively High | |||
| Electrical conductivity as µmho/cm | < 400 | 400-800 | 800 - 1600 | 1600 - 3000 | 3000 - 6000 | > 6000 | none | none |
| as mmho/cm or dS/m | < 0.4 | 0.4 – 0.8 | 0.8 – 1.6 | 1.6 – 3.0 | 3.0 – 6.0 | > 6.0 | none | none |
| Total dissolved solids as TDS mg/L | < 250 | 250 – 500 | 500 - 1000 | 1000 - 2000 | 2000 - 4000 | > 4000 | 500 | none |
| Nitrate-nitrogen as NO3-N mg/L | < 3.0 | 3.0 - 7.0 | 7.0 - 10.0 | 10 - 20 | 20 - 40 | > 40 | none | 10 |
| Nitrate as NO3 mg/L | < 13 | 13 - 30 | 30 - 45 | 45 - 90 | 90 - 175 | > 175 | none | 45 |
| Fluoride as F mg/L | < 0.5 | 0.5 - 1.0 | 1.0 - 2.0 | 2.0 - 4.0 | 4.0 – 8.0 | > 8.0 | 2 | 4 |
| Sulfate as SO4 mg/L | < 125 | 125 – 250 | 250 - 500 | 500 - 1000 | 1000 - 2000 | > 2000 | 250 | none |
| Chloride as Cl mg/L | < 75 | 75 – 150 | 150 – 250 | 250 - 350 | 350 - 500 | > 500 | 250 | none |
| Calcium as Ca mg/L | < 40 | 40 - 80 | 80 - 120 | 120 - 160 | 160 - 320 | > 320 | none | none |
| Magnesium as Mg mg/L | < 12 | 12 - 24 | 24 - 48 | 48 - 120 | 120 - 240 | > 240 | none | none |
| Sodium as Na mg/L | < 20 | 20 - 50 | 50 - 100 | 100 -250 | 250 - 500 | > 500 | none | none |
| Iron as Fe mg/L | < 0.06 | 0.06 - 0.12 | 0.12 - 0.30 | 0.30 - 0.90 | 0.90 - 1.80 | > 1 .80 | none | none |
| Manganese as Mn mg/L | < 0.005 | 0.005 - 0.010 | 0.01 - 0.05 | 0.05 - 0.10 | 0.10 - 0.5 | > 0.50 | none | none |
| Hardness as | Soft | Moderately hard | Hard | Very Hard | Extremely Hard | Brackish | ||
| CaCO3 mg/L | < 60 | 60 - 120 | 120 - 180 | 180 - 270 | 270 - 400 | > 400 | ||
| CaCO3 grains/gallon | < 3.5 | 3.5 – 7.0 | 7.0 – 10.5 | 10.5 – 16.0 | 16.0 – 23.5 | > 23.5 | ||