The Environmental Protection Agency (EPA) recommends drinking water to be at pH 6.5 - 8.5. It is important to maintain drinking water within the safe range as pH influences concentration of certain contaminants.
Since most drinking water is highly purified, the ion strength of drinking water is typically very low. It will be very difficult to accurately test the pH level of such purified water with regular pH sensors. A specialized pH electrode specifically designed for testing low ion-concentration samples is necessary for a reliable test.
Another parameter to test for is Total Dissolved Solids (TDS).
TDS basically refers inorganic salts and small amounts of organic matter that are dissolved in water. The principal constituents are usually the cations calcium, magnesium, sodium and potassium and the anions carbonate, bicarbonate, chloride, sulphate and, particularly in groundwater, nitrate.
The U.S. EPA sets the maximum contaminant level for TDS at 500 ppm. At higher levels, gastro-irritations, excessive hardness, unpalatability, mineral deposition and corrosion may occur. TDS is usually converted from conductivity with a conversion factor from 0.5 to 1.
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