Most public drinking water supplies are chemically treated in order to remove bacteria, viruses and other harmful organisms. The most common method of disinfection is chlorination, which involves treating the water with the chemical chlorine on an ongoing basis. The necessary elimination of harmful bacteria through chlorination can create harmful by-products called Trihalomethanes (THMs), which are considered a health hazard.

THMs are a group of organic compounds, which can be generated by the treatment of drinking water supplies with chlorine. They are produced by the reaction of organics with chlorine and related chemical compounds. They are not naturally occurring compounds. Drinking water regulations suggest that the concentrations of these compounds be as low as possible due to perceived health risks.

Studies in the United States have shown an association between ingestion of chlorinated by-products in drinking water supplies with rectal and bladder cancer. Health officials suggest that the risk of miscarriage is increased by 15% due to drinking chlorinated water. Such is the concern that the U.S. government is in the process of introducing a strategy to reduce the use of chlorine in drinking water supplies.

This policy is being mirrored in Europe and other parts of the world. The trend in water treatment is moving towards the use of alternative methods of disinfection. According to the EPA report, 1996, “The current degree of monitoring (TMHs) has barely begun to define the position and considerably greater effort is required without there being an undue delay”.

In general the level of THMs varies depending on the source of the drinking water. Deep wells treated with chlorine have a lower level of these by-products than surface water supplies (i.e. lakes and rivers) similarly treated. The reason is due to the significant levels of organic compounds, called tannins and humic acids, in many surface water supplies. These can give the water a yellowish hue when compared to clean filtered water. In addition the reaction between chlorine and these organic products can give the water a bad taste.

Given that many water supplies in the West of Ireland fall into surface water categories the problem of THMs should be of concern. Effective means are available for the removal of chlorine and its by-products through point-of-use in-home removal systems.

Many homes in the West of Ireland use non-chlorinated water from sources such as private wells or nearby surface water. This water should be submitted for microbiological and chemical analyses. If the water is found to contain levels of harmful bacteria, the home owner may as an alternative to chlorination, choose to have an Ultra-Violet Sterilisation system installed.

Ultra-Violet systems are recommended by County Councils as an effective method of removing bacteria from a drinking water supply. In order to conform with EU and Irish Legislation for Planning Permission or Grant Application purposes, home owners may be required to install a UV system in their home.

An Ultra-Violet System is comprised of a UV light emitting tube, similar in appearance to a household fluorescent light tube. The UV tube is placed within a quartz sleeve, which is housed inside a stainless steel chamber through which water flows. The UV light kills bacteria.

Proper application, installation and maintenance is essential for effective sterilisation of the water supply by UV systems. Of particular concern is the proper fitting of a systems failure alarm. As well, some organisms as Giardia and cryptosporidium cysts may not be killed. Water suspected of containing these organisms can be safely filtered with the use of ceramic filters or reverse osmosis systems, often in conjunction with UV systems.

Ceramic cartridge filters are becoming popular in the West of Ireland for use in unsafe water conditions. These cartridges, for reasons of cost effectiveness, are used as “point of use” drinking water only systems. The cartridge is housed in a container, which is usually installed under the kitchen sink. Drinking water from the cold water line is diverted through the ceramic filter and then flows through a separate tap installed on the counter top. Ceramic filters vary in quality and capability. The technical aspects should be carefully considered prior to installation on unsafe water.

Reverse osmosis filtration systems utilise membrane technology along with other filters. It is a relatively slow method for producing pure water, therefore most RO systems require small pressurised storage tanks. This is an effective system for the removal of Giardia and cysts as well as dissolved solids such as salts and metals; however, as with ceramic filters, indeed all water treatment systems, careful professional advice should be obtained prior to purchase.