Changing the pH of Water With a
Chemical Feed Pump or Neutralizing Filter

The Use of Soda Ash and Caustic Soda to Alter pH

Neutralizing Filters and Chemical-Feed Pumps

Neutralizing filters and chemical-feed pumps adjust the pH of water. A pH of 7 is neutral, while a pH less than 7 is acidic, and a pH greater than 7 is alkaline. Water should be as close to pH 7 as possible. Very low or very high pH water is corrosive, which can cause leaching metals from plumbing systems or forming scale in pipes. Signs of very low or very high pH water are blue-green stains from copper plumbing or red stains from galvanized plumbing.

Tank-type neutralizing filters or chemical-feed pumps that inject a neutralizing solution into the well neutralize acid water. If iron treatment is needed, the chemical-feed pump system is required. Tank-type neutralizing filters pass the water through granular calcite (marble, calcium carbonate, or lime) or magnesia (magnesium oxide). They treat water as low as pH 6. They must be installed after the pressure tank. These systems make the water harder.

For water less than pH 6, chemical-feed pumps inject a neutralizing solution of soda ash (sodium carbonate) or caustic soda (sodium hydroxide) into the well. This raises the sodium content of the water. Potassium can be substituted for sodium, but potassium is more expensive. Keep the solution tank full and adjust the feeder to provide the correct rate to result in a pH of near 7. For water between pH 4 and pH 6, use soda ash mixed at one pound of soda ash per gallon of water. Feed this solution into the well at a rate to raise the pH to near 7 at the faucet farthest from the well. For water less than pH 4, use caustic soda. This material is extremely dangerous. Wear gloves and goggles. Slowly feed a solution of one pound of caustic soda per gallon of water into the well at a rate sufficient to result in pH 7 at the faucet farthest from the well.

Neutralize alkaline water (greater than pH 7) by feeding diluted sulfuric acid in the same manner as soda ash. Use caution in making solutions from strong acids. Always add acid to water slowly. Never add water to acid: Use gloves and goggles when preparing solutions.

Excerpted from Home Drinking Water Treatment Systems, prepared by:

Glenda M. Herman
Extension Housing Specialist

Gregory D. Jennings
Extension Water Quality Specialist

Published by: North Carolina Cooperative Extension Service

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