pH / Corrosion Control

Table of Contents

pH

The ratio of acidity to alkalinity is represented by the pH of the water. The range of pH can be from 0-14. Neutral water has a pH of 7 (acidity = alkalinity) . If the pH is below 7, we say the water is acidic, and, if the pH of the water is above 7, we say the water is alkaline. We generally consider acid water as being aggressive (likely to dissolve pipes and fixtures). Very alkaline water can also be aggressive. Water with a pH between 6.8 and 8.5 is usually not very aggressive. Aggressive water causes premature failure of copper pipes, appliances and fixtures. The most common evidence of this problem is blue green staining in the fixtures. The stain is caused by

New pipe compared to one that has be corroded by aggressive water(click on image for enlarge view)

the copper that has been deposited there from the corrosion of the pipes by the aggressive water. You are actually seeing part of your copper pipes laying in the bottom of the sink when you look at this blue green stain. This corrosion can continue even if the pH of the water is above 7. To prevent this corrosion it will sometimes require the pH of the water to be raised as high as 8.

Most of the water we have in Maine has a pH of less than 7. The reason for this is the lack of CaCO3 (calcium carbonate), commonly called limestone or marble, in the bedrock and soil to naturally raise the pH of the water. CaCO3 when dissolved in water will not only raise the pH of the water but will increase the hardness by adding Ca (Calcium) to the water.

Treatment

There are two commonly used methods to raise the pH of the water in residential applications -

One is to pass the water through a tank that has ground up CaCO3 . This calcium carbonate will of be referred to as AN (acid neutralizing) media.

The advantages are-
-that the owner does not have to do anything
-the pH of the water will not rise above 7.2.

The disadvantages are -
- very low pH levels (<6.0) are often not raised high enough
- if a pH of greater than 7.2 is needed it can not be obtained
- the hardness of the water may be raised high enough to require the addition of a softener.

The other choice is to use a solution feed system. This system consists of a pump and solution tank. The pump injects a solution into the water that will raise the pH.

The advantages are-
- that virtually any pH required can be obtained
- there is no increase in the hardness.

The disadvantage is-
-that the owner must mix the solution periodically (typically once a month).

Some companies will advocate the use of a material called corrosex when the pH can not be raised high enough with CaCO3 . Corrosex is MgO (magnesium oxide - chalk). The problem with this solution is that the pH can jump as high as 11, cause a dramatic increase in the hardness of the water and cause the water to taste bitter (alkaline) or chalky. The pH attained will depend on the amount of time the water is in contact with the material. The amount of contact time will be dependent on flow. Unfortunately, the flow in a household situation is not continuous and therefore the pH will fluctuate dramatically. Lastly, the customer will typically need to have material added to the to the tank once every month or two. He can not do this himself and will therefore require frequent service calls.