Treating the water can reduce corrosion to acceptable levels, but usually does not eliminate it. Treatment depends on the cause of the corrosion.
Acidity Treatment
If acidity is the problem, installing a neutralizing filter usually works best. These filters contain fragments of calcium carbonate (limestone), marble, magnesium oxide (magnesium carbonate), or other alkaline materials that dissolve in water and on time.
Acid neutralizing filters are usually installed after the pressure tank. As water flows through the filter, the pH increases, which reduces corrosivity.
This process makes the water harder. It may also reduce water pressure.
The neutralizing material must be replenished when it dissolves. The debris can last from weeks to months, depending on the type of material, the corrosiveness of the water, and the amount of water you are using. Filters must usually be backwashed to remove trapped particles and oxidized metals.
Another way to neutralize acidic water is to add a solution of sodium hydroxide or sodium carbonate (soda ash). This is usually accomplished by installing a chemical feed pump before the pressure tank. If you are on a low-sodium diet, consider using potassium hydroxide instead of sodium salt.
This treatment system is simple and inexpensive; it does not increase water hardness or decrease water pressure. The injection rate should be adjusted to produce water with a pH of 7.5 to 8.0.
The injection unit requires a great deal of maintenance, including filling solution tanks and maintaining feed pumps. Soda ash is preferred over sodium hydroxide, which is extremely corrosive and requires special safety precautions; it should be handled only by trained personnel.
Salt Reduction
Removing high concentrations of dissolved salts from water requires a reverse osmosis system. This method may require pre-treatment of the water, and whole-house systems require large storage tanks. Reverse osmosis systems increase total water consumption by 30 to 200 percent and produce wastewater with concentrated salts.
Reverse osmosis removes 80 to 95 percent of the salt from the water entering the system. In some cases, the total dissolved salt content of the treated water may be so low that it can corrode piping components. In general, reverse osmosis water should be conveyed and distributed through non-metallic piping and fixtures.
Removing high levels of dissolved salts from whole-house water systems is usually not feasible. Instead, food-grade polyphosphates or silicate compounds can be added to the water system to control corrosivity.
These materials deposit a thin coating inside the pipes, limiting contact with water. The film dissolves slowly, so the material should be maintained at the proper level. Initially, existing corrosion may loosen and flush the entire system, making the red water problem look worse. Higher feed rates will clean the system and form a protective film. Then reduce the dosage to maintain the protective film.
Reducing Dissolved Oxygen
There is usually nothing you can do to reduce dissolved oxygen in a small water system. Installing a flexible membrane or float pan in a pressure tank will minimize water-air contact. This type of tank will also minimize standing water, which is common in highly aerated water. However, it may be necessary to inject polyphosphate or silicate compounds to protect the water system over time.
Large semi-open tanks can be used to allow air to escape, similar to the way bubbles escape in a glass of water. Since the water is no longer pressurized, a tank twice the daily water consumption and chlorination is required.
