Water Corrosion Control in Household Systems

Corrosion control is a complex science, requiring considerable knowledge of corrosion chemistry and of the system being evaluated. Corrosive water can be managed by installing pretreatment systems, installation of non-conductive unions, reducing hot water temperature, and replacing copper piping with polyvinyl chloride (PVC) or chlorinated polyvinyl chloride (CPVC). The pretreatment process treats the corrosivity of the water by changing the Saturation Index through an increase or decrease in the pH, hardness, and/or alkalinity. The resultant saturation index (SI) is typically more positive and preferably the SI is between -0.5 to +0.5. (reference)

In addition to changing the SI, one approach includes establishing a thin film of calcium or magnesium carbonate on the surface inside the piping that acts as a physiochemical barrier. The pretreatment systems typically used in application for homeowners or small private water suppliers includes either a neutralizing tank filter or caustic liquid treatment feed system. The neutralizing filter is more commonly used. The neutralizing filter uses crushed limestone, magnesia or some other mixture and as the water passes through the filter, the filter neutralizes the excess acid and results in the partial dissolution of the media. Therefore, the neutralizing filter actually increases the hardness of the water and raises the pH. The following are the chemical equations for the filter reactions:

H₂CO₃ + CaCO₃ --> Ca(HCO₃)₂
2H₂CO₃ + MgO --> Mg(HCO₃)₂ + H₂O

Another method of neutralization requires the addition of sodium carbonate (soda ash) into the system. This should be injected ahead of the pressure tank. If chlorination is used, this solution can be mixed with the chlorine solution. (reference)

One has to keep in mind that addition of soda ash may slightly increase sodium level in the drinking water, and calcium carbonate filters will increase hardness and alkalinity.

A different approach to the control of corrosion is the injection of corrosion inhibitors, such as polyphosphates and silicates, to create protective films on plumbing components. Selection of non-corrosive plumbing materials, e.g. PVC or CPVC, will help. Since corrosion increases with elevated temperatures, water heaters should be set only as high as necessary and temperatures above 30°C are not recommended.

Corrosion associated with other chemicals like hydrogen sulfide and dissolved oxygen must be handled differently. For example, hydrogen sulfide can be treated by activated carbon filtration or chlorination.

Sodium in drinking water

In drinking water, a sodium level of greater than 20 milligrams per liter (mg/L) is not harmful to the average person's health. However, if you suffer from high blood pressure, heart disease or kidney disease, and the sodium level of your water sample is higher than 20 mg/L, it is recommends that you contact your doctor for advice. (reference)

In the meantime, you can take steps to lower the sodium level in your drinking water. If you own a water softener make sure your drinking water is taken from a tap not connected to the system. Otherwise, switch to a source of drinking water that you know is low in sodium. If you are feeling frugal you should talk to your local professional about alternatives to water softeners that have no salt or potassium additives so you can utilize your tapwater.

NOTE: Boiling does not remove sodium from water and in fact may increase the sodium concentration.

The sodium in drinking water contributes very little to average adult's sodium intake of 4000 mg to 6000 mg daily. Processed foods - e.g. popular snacks, fast food items, canned goods and other prepared foods - are the major sources of sodium in the Canadian diet. A hamburger (double patty) with condiments provides about 800 mg sodium; one dill pickle, over 800 mg; a cup of chicken noodle soup (made from canned concentrate), almost 1200 mg; a sub made with cold cuts, 1650 mg; one ounce of potato chips, over 210 mg. By comparison, 1.5L of drinking water at a sodium concentration of 50 mg/L would contribute 75mg of sodium to a person's overall daily intake.

Individuals suffering from hypertension or congestive heart disease may require a sodium restricted diet, in which case the concentration of sodium in drinking water may become significant. Drinking water concentrations of sodium that exceed 20mg/L may need to be taken into consideration in dietary planning for individuals prescribed a regime that significantly restricts sodium intake. This is most likely to be the case when a patient requires a diet with a very strict level of sodium restriction, e.g. a diet that provides a total sodium intake of no more than 500mg/day.