Understanding corrosive water is not complicated. The corrosiveness of water is largely due to three factors; the pH, the amount of alkalinity, and the hardness of the water. Water in nature will be either acidic, neutral, or basic. pH is a measure of how acidic or basic the water is.
It is expressed as a number from 0 to 14. Neutral water, which is neither acidic or basic, has a pH of 7. As pH values decrease from 7 to 0, the acidity of the water increases; pH values from 7 to 14 show increasing basicity. Well water usually has a pH between 5 and 9.
Alkalinity is a measure of the water’s ability to neutralize acids and bases. It is mostly due to the amount of naturally occurring carbonate and bicarbonate compounds which have been dissolved by the water. Because the alkalinity can neutralize both acids and bases, it allows the water to maintain a stable pH. This process is known as buffering. Hardness is due to the amount of calcium and magnesium dissolved in the water.
“Hard” waters are less corrosive than “soft” waters. Hardness helps to prevent corrosion by adding to the buffering ability of the water and by forming a protective film on the pipe walls. For most domestic water, corrosion will be minimal when the pH is near neutral (7), the alkalinity is greater than 30 milligrams per liter (mg/1), and the hardness is more than 50 mg/l.
The Cause of Corrosive Water
The pH, alkalinity and hardness of a water are a result of the amounts and types of minerals dissolved into the water from the surrounding soils and rocks. Water’s natural acidity is caused by the presence of carbonic acid and carbon dioxide.
When the amount of alkalinity and hardness are low, the water cannot be neutralized and the soft water may attack any exposed metal surfaces.
Affects of Corrosive Water
Corrosive water will attack any exposed metal surface, slowly dissolving the metal into the water. Constant exposure to corrosive water will noticeably shorten the life of household plumbing, eventually causing pin-holes to appear in the pipes.
Corrosion will occur at any place in the water system where water contacts metal. This includes pipes, faucets, well casings, pressure tanks, and the well pump itself. With copper plumbing, corrosion will cause blue-green stains in sinks and tubs, and will give the water a bitter, medicinal taste.
The taste will be most noticeable when the water has been standing in the pipes for long periods of time, such as overnight. Anytime a taste is noticed, or when the water has been in contact with the plumbing for longer than six hours, the water should be allowed to run for several minutes before using. This flushes any metal-containing water from the pipes.
Corrosive (Acidic) Water
The corrosion of steel or galvanized metal will cause a rusty stain in fixtures, give the water a metallic taste, and may produce cloudy water on occasion. In addition to damaging the water system, corrosive water can also interfere with other water treatment. Iron and manganese cannot be easily removed from acidic water. In this case, the acidity must be neutralized prior to the iron removal treatment.
Treatment of Corrosive Water
1. Adjusting pH:
This method uses a small metering pump and mixing tank. The metering pump adds small amounts of a mixture of soda ash and water to the well water whenever the well pump is running. The soda ash (sodium carbonate) raises the pH and the alkalinity of the well water, chemically neutralizing the acidity. The use of soda ash will not increase the hardness of the water. However, this method can be used with almost any pH level. The above treatment method typically what is done to bottled water after it been stripped by an RO is the owner is interested in tricking the public a little! I don’t like it at all… manipulating the public to a large degree. (OK bottled water guys, don’t email me… you know exactly what I am saying)
2. Neutralizing Filters:
These are essentially a pressurized tank containing a filter bed of calcium carbonate or calcite. As the acidic water passes through the filter, the carbonic acid and carbon dioxide combine with the calcium carbonate neutralizing the acidity. Because the filter bed is composed of a calcium compound, neutralizing filters will increase the hardness of the water, as well as increase the pH and alkalinity. Neutralizing filters work best at a pH between 6 and 7. If the pH is between 5 and 6, a magnesium oxide must be added to the filter bed to adequately neutralize the acidity. They should not be used with a pH below 5. Neutralizing filters must be backwashed periodically to remove sediments trapped within the filter bed. Most manufacturers offer both a manually operated and an automatic backwash cycle.
3. Polyphosphates (Micromet, Shan-No-Coor, etc.):
These compounds deposit a protective layer on exposed metal surfaces. They do not change the acidity of the water. Polyphosphates work best within a pH range of 6.8 to 7.4. It may take as long as eight weeks for the protective coating to form