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How to Reduce Corrosion for Galvanized Water Pipe?

Treating your water can reduce corrosion to acceptable levels, but generally will not eliminate it. Treatment method depends on what is causing the corrosion.


Treating for acidity


If acidity is the problem, installing a neutralizing filter usually works best. These filters contain chips of calcium carbonate (limestone), marble, magnesia (magnesium carbonate), or other alkaline materials that dissolve as the water neutralizes.

Acid-neutralizing filters are usually installed after the pressure tank. As water flows through the filter, pH increases which decreases corrosivity.

This process makes the water harder. It also may decrease water pressure.

The neutralizing material must be replenished as it is dissolved. The chips can last from weeks to months, depending on the type of material, how corrosive the water is, and how much water you use. The filters usually must 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 done by installing a chemical feed pump before the pressure tank. If you are on a low-sodium diet, consider using potassium hydroxide instead of the sodium salts.

This treatment system is simple, and inexpen-sive; it does not increase water hardness or reduce the water pressure. The injection rate should be adjusted to produce water with a pH of 7.5 to 8.0.

Injection units require significant maintenance that includes filling solution tanks and maintaining the feed pump. Soda ash is preferable to sodium hydroxide, which is extremely caustic and requires special safety precautions; it should be handled only by trained individuals.


Reducing salts


Removing high concentrations of dissolved salts from water requires a reverse osmosis system. This method can require that the water be pretreated, and whole-house systems require large storage tanks. Reverse osmosis systems increase overall water use by 30 to 200 percent and generate wastewater with concentrated salts.

Reverse osmosis can remove 80 to 95 percent of salts from the water entering the system. In some cases, treated water may be so low in total dissolved salts that it corrodes plumbing components. Generally, reverse osmosis water should be transferred and dispensed through non-metallic pipe and fixtures.

It is generally not feasible to remove high levels of dissolved salts from whole-house water systems. Instead, food-grade polyphosphate or silicate compounds can be added into the water system to control corrosiveness.

These materials deposit a thin coat inside the pipe which limits contact with the water. The film will slowly dissolve so the material should be maintained and fed at proper levels. Initially, existing corrosion can loosen and flush through the system making the red water problem seem to be worse. A higher feed rate will clean the system and establish a protective film. Then reduce the amount to maintain the protective film.


Reducing dissolved oxygen


Often, there is little you can do to reduce dissolved oxygen in small water systems. Installing a flexible membrane or a floating disc in the pressure tank will minimize the water’s contact with air. This type of tank also minimizes waterlogging, which is common with highly aerated water. However, it may be necessary to inject polyphosphate or silicate compounds to protect the water system over the long term.

A large, semi-open storage tank can be used to allow air to escape similar to the way bubbles escape in a drinking glass. This requires a tank twice the size of the daily-use rate and chlorination since the water is no longer pressurized.