Those Blue-Green Stains

Water supply systems that exceed the US EPA action level for copper must take a number of corrective measures.
Those Blue-Green Stains
Water supply systems that exceed the US EPA action level for copper must take a number of corrective measures.

The Florida Gateway College water program had an inquiry from a public works director of a small community about copper in drinking water. A customer at a convenience store had seen blue-green stains on plumbing fixtures around the soda dispensing equipment. Both the customer and the public works director were concerned.

We explained that these stains do usually indicate the presence of copper in the water. Some factors that can increase copper levels in drinking water are the water’s acidity, soft water, high chlorine residuals, long detention times in pipes and elevated water temperature.

EPA standards

The Safe Drinking Water Act requires the U.S. EPA to determine the levels of contaminants in drinking water at which no adverse health effects are likely. These non-enforceable goals, based solely on possible health risks and exposure over a lifetime, are called maximum contaminant level goals (MCLG). The MCLG for copper is 1.3 mg/L.

For most contaminants, the EPA has an enforceable maximum contaminant level (MCL), based on the MCLG. MCLs are set as close to the MCLGs as feasible. The agency considers cost, benefits, and the ability of public water systems to detect and remove the contaminant using suitable treatment technologies.

However, because copper contamination of drinking water often results from corrosion of customers’ plumbing, the EPA has established a treatment technique rather than an MCL for copper. A treatment technique is an enforceable procedure or level of technology that water systems must observe to ensure control of the contaminant.

Sources of copper

Copper most often gets into drinking water through corrosion of copper pipes, fixtures and fittings in customers’ homes; brass faucets can also be a source.

Natural copper levels in surface and groundwater are generally very low. High levels may be related to mining, farming, manufacturing, and municipal or industrial wastewater releases into rivers and lakes. Discharges of copper into sewer systems from some residential areas have been found. Copper compounds also occur in agricultural fungicides, algaecides (for water reservoirs), food supplements and fertilizers.

Copper as a nutrient

Copper in small amounts is an essential nutrient for living organisms, including humans. Food sources of copper include shellfish, nuts, grains, leafy vegetables and stone fruits. Typical sources of copper from food range from less than 2 milligrams to 5 milligrams per day.

Copper in drinking water can add up to 45 percent more copper to a person’s diet than what is in food sources. Generally, the body excretes about half the ingested copper daily. Copper is widely distributed within body tissues but accumulates primarily in the liver and kidneys.

Too much copper can cause adverse effects. For example, a single dose of 15 milligrams of copper can cause nausea, vomiting, diarrhea and intestinal cramps. Drinking water that exceeds the action level over many years has been associated with liver damage and kidney disease.

People with Wilson’s and Menke’s diseases — genetic disorders that result in abnormal copper absorption and metabolism — are at higher risk from copper exposure than the general public.
The human body’s natural mechanisms maintain proper levels of copper, but children under one year old have not developed this mechanism and are more vulnerable to copper’s toxic effects. The EPA set its action level of 1.3 mg/L for copper to protect against acute toxic effects. However, that limit does not protect the most sensitive people.

Taking care

The longer water stands idle in copper pipes, the more copper it is likely to absorb. Newer homes with copper pipes may be more likely to have a problem. Over time, a coating forms in the pipes that can isolate the water from the copper. In newer homes, this coating has not yet developed.

Where copper absorption from pipes is a concern, water that has not been used for more than six hours should be cleared from the pipes before being used for drinking or cooking.

The pipes can be cleared by letting the cold-water faucet run until the water feels cold, usually 30 to 60 seconds. Hot water dissolves copper faster than cold, so water for drinking or cooking should not be drawn from the hot-water tap, especially if it will be used to make baby formula.

The supply side

Water supply systems that have exceeded the action level for copper must take a number of corrective steps. The treatment technique regulation for copper in the Lead and Copper Rule requires water systems to control the water’s corrosivity. It also requires systems to collect tap samples from sites served by the system that are more likely to have plumbing materials containing copper or lead. If more than 10 percent of tap water samples exceed the copper action level of 1.3 mg/L, water systems must take additional steps to reduce water corrosiveness.

These include testing the source water for contamination and treating the water to make it less corrosive or less likely to absorb copper from the plumbing. Treatment methods such as reverse osmosis, ultrafiltration, distillation and ion exchange can remove copper.

In the case of the soda machine, college representatives explained that there is a great risk of copper contamination from carbonated and acidic beverages that have been in contact with copper tubing, fixtures or containers. The carbon dioxide used in soft drink dispensers is under pressure. Where it is mixed with the incoming water, there is a potential for carbon dioxide to backflow through the incoming water supply. The carbon dioxide then can corrode the copper plumbing, which in turn can add copper to the soft drinks.

The surest way to prevent carbon dioxide from contacting copper pipes is to install a reduced-pressure backflow prevention assembly. This assembly should be installed on the incoming water supply pipe before the carbon dioxide injection point. Copper piping should not be used past the injection point.

About the Author

John Rowe, Ph.D., is a professor of Water Resources at Florida Gateway College in Lake City, Fla. He can be reached at john.rowe@fgc.edu.



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