Water Pollution

Water pollution is the loss of any beneficial uses of water (actual or potential) through contamination by human activity. There are, of course, a wide variety of beneficial uses of water - from drinking and domestic use, to use in industry, in agriculture and for fishing and swimming. If water is rendered unsuitable for any of these possible uses, then it is polluted. The degree to which it is polluted will vary depending on the level of contamination present. Water may become unsuitable for use either temporarily or permanently from natural causes. However, it is human involvement that causes pollution.   

Of course it is not reasonable to expect that water occurring in its natural form will be immediately suitable for all uses. You would not expect to be able to drink water straight from every river you happen across; all sorts of microbiological substances could be present. At the same time, this water is not necessarily polluted. However, if, as a result of human activity and even after treatment, this water was still unsuitable for some use (such as drinking), then it would be considered polluted.

Pollution occurs on a regular basis worldwide. However, many changes have been made in the last century to address this global environmental issue. Incidences of water pollution can be caused by accidental or deliberate discharge of pollutants. Examples of some sources of pollutants are sewage plants, creameries, food production waste products, silage making and manure spreading.

Urban and Rural Water Pollution

Pollution can be caused by many different things in many different areas. In cities, outflows from sewage treatment and industrial plants are the main causes of pollution. Also, run-off from roads can wash oil into nearby watercourses. The expanse of concrete infrastructure prevents rainwater, snow, etc. from soaking into the ground. In rural areas, much of the pollution originates from animal wastes and commercial fertilisers. To a lesser extent, groundwater contamination also occurs in this sector as a result of inadequate percolation at septic tanks and from leaching of water soluble plant nutrients from the soil.

Groundwater Pollution

Groundwater is the water that trickles through the soil and into underlying rocks during the Water Cycle. Once in the bedrock the water moves slowly through and is stored in the pores or cracks in the rock. If enough water is stored in this way in a bedrock deposit, it is referred to as an aquifer. Groundwater seeps up and emerges at ground level by coming out at springs or by flowing into rivers. It can also be pumped up from the aquifers. Approximately 26% of Ireland 's drinking water supply is provided by groundwater or springs, if both public and private supplies are taken into account. Groundwater is not usually subjected to any treatment and groundwater monitoring networks are in place to check if levels of purity are in line with drinking water standards.

The Environmental Protection Agency has a Groundwater Monitoring Programme to monitor groundwater quality using a selection of public and private wells and springs countrywide. Particular consideration has been given to the concentration levels of certain pollution indicators such as ammonium, nitrates, phosphates and faecal coliforms (a bacteria found in faeces).

For further information on Ireland's water, see the EPA's full report, Ireland's Environment 2012


Eutrophication is the increase in chemical nutrients in an ecosystem which results in excessive plant growth and decay.  Nutrients are, of course, a requirement in order for aquatic plants and animals to grow; but unnaturally high levels of nutrients cause excessive growth. The water becomes cloudy, changing colour to a shade of green, yellow, brown, or red. When the plants die, they are decomposed by micro-organisms including bacteria which consume oxygen dissolved in the water in the process. A large increase in the number of decomposing bacteria leads to a sharp decline in oxygen levels. Certain fish such as salmon and trout need high levels of dissolved oxygen to survive and so a substantial number of fish kills are caused by eutrophication.

This process can cause severe reductions in water quality and damage to fish and other animal populations. In most cases, the primary cause of eutrophication is phosphorus, with nitrates as the secondary cause. The impact of nitrates is increasing however, particularly in coastal waters. 

In Ireland , approximately 15% of our lakes are significantly affected by eutrophication.  Almost 19% of coastal water areas have been found to be eutrophic by the EPA and the nutrient levels on rivers have also been found to be quite high.

Eutrophication can occur naturally, but more commonly this process is caused by a number of human influences such as the release of sewage effluent, and run-off from fertilisers.

Initiatives to control eutrophication take a number of different forms. Legislation at European and national level has been enacted to control the spreading of animal waste. The standard of wastewater treatment in Ireland has risen in accordance with the European Wastewater Directive and more rigorous controls have been put in place for the installation and maintenance of septic tanks.

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