Q

Dear Professor,

We see severe copper corrosion in conjunction with new homes and chloraminated water. All of our natural California blonds have gone green. Raising the pH with calcite does not solve the problem. Do you have a proven method for protecting old and new copper pipes?

                                                                                                – California

A

Yes, there can be a causal connection with chloramination (or chlorination) and copper corrosion. Chloraminated water leaving a municipal treatment plant must be in conformance with EPA standards both in the plant design and with a properly planned and carefully managed monitoring system. If uncontrolled the problem might be the chloramination itself. If in compliance there should not be a corrosion issue.

Chloramine, typically monochloramine, has been used for many years as a “residual” or distribution system disinfectant for two reasons. It is a weak disinfectant, but more stable than chlorine and, as such, extends further into distribution systems. It also has the property of creating fewer chlorine by-products. Chlorine and other stronger disinfectants are usually used as the primary, or in-plant, disinfectants.

Without proper design, or redesign of an older distribution treatment, the incorrect ratio of ammonia and chlorine may lead to nitrification (converting ammonia to nitrite, then to nitrate) and corrosion of lead and copper in the system. Nitrification within the distribution system can also occur in the presence of nitrifying (or ammonia-oxidizing) bacteria. Occasional chlorination is sometimes used to control the latter. Warm water as well as extended transit and storage time during distribution can increase nitrification. As an additive, the chlorite ion can also control nitrification.

I know of no single-proven method for copper corrosion because the causes are many. There is no water analysis provided in your question, but your pH elevation would often be effective, even though there are several other causes of corrosion in copper. A few other causes are acidic pH, oxygen, dissolved oxygen, excessive flow velocity, galvanic action, hot recirculating water, TDS, chloride, sulfate and others. Try to eliminate or, at least consider, these other causes.

Troubleshooting techniques include the installation of removable sections of hot and cold copper tubing to be periodically removed and cut in half lengthwise for inspection. Analyses for copper ions in suspected sections of pipe and in samples of inlet and outlet water heater pipes is recommended. The AWWA publication, Optimizing Chloramine Treatment, Second Edition, states that both chlorine and chloramine accelerate the corrosion of copper alloys at a pH of 6 but have minimal effect at a pH of 8. It states that chlorine is more corrosive than chloramine; however, chloramine extends further into the distribution system, which may be a factor. This publication is very clear that other water conditions may have a major effect on the potential corrosion of copper.

A bulletin on “green hair” was published by the Indianapolis Water Company (the water utility), February 1994, called “blue water stains and green hair,” which does blame copper corrosion but it attributes it to “electrical systems applying current to the plumbing.” They further make the following controversial statement, “The plumbing must not be used as part of the electrical circuit” (emphasis theirs).

                                                                                                        David M. Bauman

 

Q

Many point-of-use (POU) devices contain silver in some form. What is its function and what claims can be made about it by marketers of POU products?

 

A

Silver is frequently employed in POU devices, especially those that involve carbon blocks and some commercial ceramic filters, and also locally made clay/ceramic filters; the latter are commonly used in developing country low tech applications.

Several forms of silver are used in water treatment including silver metal, silver salts (e.g. nitrate), silver oxide, glasses, colloids, zeolites and nanoparticles. The consensus seems to be that silver exerts its biological effects on microorganisms by releasing silver ions (Ag+) that can interact with the organism by binding to sulfur thiol groups in proteins that contain the amino acid cysteine, or internally within the cell by producing active oxygen species (superoxide), and binding to DNA and displacing hydrogen bond linkages between the DNA bases.

Silver’s use in water treatment devices and other applications is regulated as a pesticide in the U.S. by the Environmental Protection Agency (EPA) under the Federal Insecticide Fungicide and Rodenticide Act (FIFRA). Pesticides are broadly defined as any substance that is intended for preventing, destroying, repelling or mitigating any pest. So silver’s role as a biocide (kill) or biostat (growth retardation) puts it in the pesticide category, and its commercial uses in water treatment must be registered by the EPA. The amount of silver that can be released into the water is up to the 100 microgram per liter range, but the typical water concentration from a device is much lower. Silver can cause a condition called argyria, which is a graying of the skin, from excessive long term consumption; the oral reference dose is 0.005 mg/kg/day, which is equivalent to 175 micrograms per liter.

The scientific data on silver’s performance as a biocide or biostat in water is mixed and, therefore, regulators have been cautious regarding performance claims. There is a large data base that indicates that silver can be a biocide or biostat, but there are inconsistencies in results and the biocidal effects are usually slow, i.e. much slower than has been demonstrated for chlorine. One study reported greater than 6 log reduction of several bacteria in eight to nine hours by silver at 100 micrograms per liter. The effects would also be concentration dependent and it also requires contact between the silver and the microorganism, so the effects would likely deteriorate with time and as biofilms might form.

The EPA regulated registration claims for a water treatment device must be on the label, and they are limited to inhibiting the growth of microorganisms in the device, and removing objectionable odors from the water; the product cannot claim to be a biocide that removes pathogens from water. Generally, the microorganism growth being suppressed would be the usually non-pathogenic heterotroph organisms that grow in stored water in the absence of a residual disinfectant. Filters that are capable of physically removing protozoa, like cryptosporidium, by size exclusion filtration or other mechanisms, can claim that, but not due to the presence of silver.

There are several studies showing significant reductions of coliforms and protozoa in locally made clay ceramic filters impregnated with silver; however, there was not a clear finding of the specific role of silver. Mechanical screening that can include size exclusion filtration, as well as adsorption, sedimentation, turbulence and diffusion in these types of devices could have contributed to the microbial reductions that occurred in the filtered water.

So, silver does have antimicrobial effects in water, but it tends to be slow acting and its possible role in eliminating pathogens is not relied upon, nor can it be claimed by, POU water treatment devices that are registered for use in the U.S.

                                                                                                                    – Dr. Joseph Cotruvo

David M. Bauman, CWS-VI, CI, CCO, is technical editor of Water Technology® and a water treatment consultant in Manitowoc, Wis. He received his B.A. from the University of Illinois in Industrial Design. He can be reached by email at: dp-bauman@sbcglobal.net.

 

Dr. Joseph Cotruvo is president of Joseph Cotruvo and Associates, LLC, Water, Environment and Public Health Consultants. He is a former director of the U.S. EPA Drinking Water Standards Division.