Drinking water, and water for personal use, including water in swimming pools needs treatment to control bacterial growth and prevent transmission of infection from one individual to another. Industrial heating, ventilating and air conditioning units also require recirculating water systems which have to be treated to prevent the formation of scale, corrosion and biological fouling.
Industrially, recirculating waters are treated with a variety of strong chemicals to remove and control the growth of algae, bacteria and fungi.
Chlorine is commonly used in swimming baths and has quite a pungent smell, and in many cases causes the eyes to sting. For large scale operations chlorine cylinders are used. The chlorine reacts with water to form hypochlorous acid and chlorine ions.
Cl 2(gas) + H 2O (water) » HOCl + H + + Cl –
For small scale operations chlorine cylinders are inconvenient and dangerous to handle. In such cases the hypochlorous acid (HOCl) is generated from calcium hypochlorite, Ca(OCl)2 by reaction with water. Problems arise when the acidity of the water is not closely monitored. Too high an acidity can cause corrosion to circulating equipment, whilst too low an acidity promotes the formation of ammonium derivatives, especially NCl3 that is a powerful eye irritant.
In drinking water, chlorination is used, except when there is present a high concentration of phenol, or one of its derivatives. Chlorine will then react with the phenols to produce chlorinated phenols that have an offensive odor and are toxic. If phenol content is high, chlorine is not used and chlorine dioxide gas is substituted. Chlorination will also result in the production of a group of organic compounds known as trihalomethanes, the most common of which is CHCl3, chloroform. Chloroform can be produced by the reaction of hypochlorous acid with the organic pollutants in the water. Chloroform levels have to be kept below 100 ppb for safety in drinking water.
More recently biocides have been introduced into water purification. These work well but pose threats to the personnel involved in using them. When water has subsequently to be disposed of, the biocides present an ecological danger, and have to be dealt with professionally to avoid contamination of rivers and watercourses.
On the other hand you and I need copper to stay healthy, as it is needed in the formation of enzymes in the body which control how the body gives us energy to work, and in the function of the nervous system. There are problems associated with copper deficiency however that can be remedied by taking copper-containing tablets as a nutritional supplement.
It is well known that copper is toxic towards bacteria. A recent article in Innovations reprinted from Diagnostic Medicine compared the effectiveness of brass and copper hardware (door knobs, push plates) with that of stainless steel. The conclusion was that although stainless steel appears clean it would support bacterial growth, whereas copper disinfected itself in about 15 minutes and brass in about 7 hours. In a different field copper-nickel clad plates were used by the International Copper Association (ICA), to clad Florida fishing boat hulls. The cladding prevented the growth of crustaceans on the hull reducing maintenance and also drag through the water. The first effect saved time and money and the second increased fuel efficiency.
Copper vessels have been used for the storage of water in part because copper is formed easily into hollow vessel, and in part because the copper keeps water free from growth so that it remains healthy to drink.
Bordeaux mixture, of which copper sulphate is the main ingredient, has been used as a fungicide since the early 1880s, especially to treat grape vines and orchard trees.
The current innovation is an extension of this effect, using copper in solution to kill bacteria in the water.