Acid: a substance with a pH of less than 7.0, which releases hydrogen ions when dissolved in water. Acids tend to dissolve metals and impart an unpleasant taste to drinking water.
Acidity: The low pH of a medium such as water, as measured by titration with a standard solution of sodium hydroxide and expressed either in parts per million or milligrams per liter of calcium carbonate equivalent.
Activated Carbon: Also called activated charcoal, a porous, granular material produced by subjecting coal to high temperatures without oxygen. It is useful in water conditioning as a filtration material to bond to, or adsorb, organic matter and certain dissolved gases.
Alkalinity: The capacity of a medium such as water to neutralize an acid. Also, the measure of how much acid can be added to water without causing a significant change in pH.
Anion exchange: The process by which anions in solution are exchanged for other anions using an ion exchanger. In demineralization, bicarbonate, chloride and sulfate anions are exchanged for hydroxide anions from the anion exchange resin.
Arsenic: A toxic, odorless, tasteless semi-metal element which was once used in products like insecticides, pesticides and paints and also has a number of natural sources in the environment. It is found in significant concentrations in drinking water in many locations, notably in the northeastern US. Like many contaminants that enter drinking water supplies, arsenic is potentially hazardous at high levels and well owners are wise to test their water for its presence.
Automatic water softener: A water softener controlled by a timer which automatically runs through backwash and/or regeneration cycles at pre-determined intervals.