From the U.S. EPA website:
The pH scale measures the logarithmic concentration of hydrogen (H+) and hydroxide (OH-) ions, which make up water (H+ + OH- = H2O). When both types of ions are in equal concentration, the pH is 7.0 or neutral. Below 7.0, the water is acidic (there are more hydrogen ions than hydroxide ions). When the pH is above 7.0, the water is alkaline, or basic (there are more hydroxide ions than hydrogen ions). Since the scale is logarithmic, a drop in the pH by 1.0 unit is equivalent to a 10-fold increase in acidity. So, a water sample with a pH of 5.0 is 10 times as acidic as one with a pH of 6.0, and pH 4.0 is 100 times as acidic as pH 6.0.
With a pH value of less than 7.0, acidic water is one of the most common causes of corrosion in private water systems. Acidic water is often fine for drinking or household use, but contains dissolved carbon dioxide gas and is low in buffering calcium minerals.
Symptoms of acid water include corrosion of fixtures, pinhole leaks in plumbing, and blue or rust-colored staining (from copper or iron pipes, respectively). Without treatment, acidic water can become contaminated with copper, lead and other metals from piping, fixtures and appliances, making it unsafe for ingestion and impractical for household use.
Testing your pH can be accomplished rather easily at home, or in a lab. If you choose to send a water sample to a lab, make sure it will arrive within 2 hours of collection, as the pH will change (begin to approach 7.0) as carbon dioxide from the air dissolves in the water. You can use a pH meter to digitally test your water’s pH by measuring your its electric potential (an indicator of hydrogen ion activity), or you can use color comparator strips which will change colors based on your water’s pH level for comparison to a standard color chart in which certain colors represent certain pH levels.
Treatment of acidic water is accomplished by neutralizing the water with an automatic neutralizer filter. These water filter tanks are generally filled with a blend of calcium and magnesium carbonates called calcite. Calcite is made from naturally occurring minerals which dissolve in water to reduce its corrosivity. More calcite can be quickly and easily added to the neutralizer filter tank, typically once per year for most residential applications, with no special tools required. This type of neutralizer also acts as a filter to remove sediment and small amounts of iron.
In some cases, acidity in water is caused by mineral acids instead of dissolved carbon dioxide. These acids sometimes have natural origins, but can also occur in mining or other industrial waste. Treating this type of water, whose pH is often less than 5.0, requires using a soda ash feeder, and in some cases injection of sodium hydroxide.
View our water test kits, pH meters, calcite neutralizers, and more in our online store, and visit our resources page to learn more about all sorts of city and well water contaminants and treatment methods.