As water sources can be exposed to different things like weather conditions, farming or commercial runoff, they can easily become contaminated. Due to the risk of contamination, drinking water must undergo a complex treatment process to ensure it is clean and safe to use.

Depending on your public water supply, your drinking water may be sourced from a combination of ground water sources (such as boreholes, springs and wells) or surface water sources (such as rivers and lakes).
Depending on the source type, water needs to undergo a number of treatment processes to meet the required level of quality as set out in the European Union Drinking Water Regulations 2014 legislation.

The following is an outline of the steps involved in treating drinking water:

Abstraction and Screening: Raw water is taken from the source e.g. a river or lake and is passed through an intake point at a water treatment plant fitted with a screen to prevent larger items (e.g. sticks, fish or stones) from entering the water treatment plant.

Coagulation: As the raw water enters the treatment plant, a chemical called a coagulant is added. This helps to bring and bind particles together in the water. Sometimes pH correction chemicals such as an acid or an alkali are also added to ensure the pH is at the optimal level. The coagulation process is helped by a rapid (flash) mixing process.

Flocculation: A second chemical called a flocculant is then added to the water. This is used to further bind the small coagulated particles in the water into a larger accumulation or build-up called a ‘floc’.

Settlement: The water then enters a large settlement tank. The tank fills slowly from the bottom allowing the floc particles to settle and form what is called a ‘sludge blanket’. The sludge blanket is drained regularly in small amounts which ensures that the sludge blanket is maintained at a constant level and does not rise to the top of the tank.

Filtration: The water which flows from the settlement tank is now much cleaner; however it has to undergo a filtration step. This is usually done in a rapid gravity sand filter. The sand filter contains different layers of graded sand and is extremely effective in filtering the water to a high degree of clarity.

Disinfection: The final stage in the drinking water treatment process is to disinfect the water. This is to ensure that any bacteria which may have survived the various treatment stages are destroyed. This is typically done using chlorine. Chlorine is added to the water either in liquid or gas form, with the dose being carefully controlled. Some treatment plants also pass the final drinking water through Ultraviolet Light (UV treatment).

Storage: After undergoing the treatment process, the treated drinking water is then pumped to a storage reservoir, which is usually located on high ground. From here, the water flows by gravity into the distribution network. The treated drinking water flows through various mains pipes in the distribution network before finally passing through a service pipe and into your home.

Please see our Why Value Water page to watch the steps your drinking water goes through from cloud to glass.

Each Local Authority has a sampling team who take water samples at both domestic and non-domestic premises on behalf of Irish Water. All water samples are tested in line with the requirements set out in the EU Drinking Water Regulations 2014 legislation. This legislation defines what parameters are to be tested for, and how often. The testing frequency for a public water supply depends on the size, i.e. the population served and the volume of water supplied. Water samples are taken from the main source of drinking water for the premises (which is typically the cold water tap at the kitchen sink). Irish Water is legally obliged to submit all drinking water quality results for compliance testing to the EPA on an annual basis.

Drinking water quality is measured by taking samples and testing the drinking water within an area for various parameters. Parameters are the measurable factors that set the standards or guidelines for the quality of drinking water.

The parameters tested in drinking water are outlined in the European Union Drinking Water Regulations 2014. This legislation specifies the standards (known as parametric values) that must be met to ensure drinking water quality is of an acceptable standard. We are initially publishing all results for 11 drinking water parameters and we intend to expand this list on a phased basis, over the coming months.

Drinking water quality parameters are categorised into 3 groups - microbiological, chemical, and indicator.

Microbiological parameters:
There are two microbiological parameters defined in the drinking water regulations – E. coli and enterococci. The presence of these parameters in drinking water may indicate that a contamination event has occurred either at source or within the water distribution network. Please see our parameters page for more information.

Chemical parameters: 
Examples of chemical parameters in drinking water include nitrate, lead, and THMs. Exceedances for chemical parameters can result in water restrictions being put in place following a consultation with the HSE. Please see our parameters page for more information on each of these parameters.

Indicator parameters:
Indicator parameters are usually tested for along with microbiological and chemical parameters in a water sample. Examples of indicator parameters include coliforms, turbidity and iron. These parameters may not pose a risk on their own, but they can indicate the presence of other potentially more harmful parameters in a water sample. Please see our parameters page for more information.

A drinking water exceedance is a result from a drinking water sample which is above the acceptable limit, as set out in the European Union Drinking Water Regulations 2014 legislation.

Irish Water has a compliance monitoring programme in place for every public water supply in the country to ensure that drinking water is adequately monitored and complies with legislation. When any drinking water exceedance occurs, Irish Water notifies the Health Service Executive (HSE). When an exceedance occurs for microbiological or chemical parameters Irish Water will also notify the Environmental Protection Agency (EPA). All parameter exceedances are fully investigated to determine the cause and to ensure that appropriate corrective actions are carried out.

Where the HSE deem an exceedance to be a risk to public health, the customers within the WSZ (or a smaller area within the WSZ) are notified with a Water Restriction Notice or a Boil Water Notice. All exceedances are fully investigated to determine the cause and to ensure that appropriate corrective actions are carried out.

Certain parameters in a drinking water sample may not be displayed due to the sample type. The two main types of drinking water samples taken when monitoring public water supplies are ‘check’ and ‘audit’ samples. Audit samples are more comprehensive and include more parameters than a check sample. A drinking water quality parameter may be tested for in a full audit sample, so it will not then be included in a check sample and therefore will not display in the table for certain time period.

Tests which may not have been not carried out as part of a particular sample type may be labelled as:

“NT” – Not Tested
“NM” – Not Measured
“NR” – No Result
“NS” – Not Specified

If a sample taken is unsuitable or deemed invalid, it may display as:

“SC” – Sample Contaminated
“Error” – Error
“RNV” – Result Not Valid

A boil water notice is an instruction issued to the public if the water supply within a certain area is not guaranteed to be at the quality standards required by the EU Drinking Water Regulations 2014 and is not safe to drink without boiling and cooling first. A boil water notice is typically issued following a contamination event within the water supply or a failure in the water treatment process. Boil water notices are both issued and lifted on the advice of and in consultation with the HSE.

If you have received a boil water notice and have any queries or concerns about your water supply, please call us on 1850 278 278.

A water restriction notice is an instruction issued to the public if the water supply within a certain area is not guaranteed to be at the quality standards required by the EU Drinking Water Regulations 2014 and either not safe to drink or use, as boiling it will have no effect on removing the contaminant.

There are several different types of water restriction notices that may be issued. The most common examples are:

  • Do Not Consume notices are issued where water should not be used for drinking or cooking but can be used for personal bathing or household cleaning activities etc.
  • Do Not Use notices are issued where water should not be used for any consumption, bathing or household purposes.
  • Targeted water restriction notices can be issued with important messaging and instructions for particular members of community e.g. pregnant women, the elderly, infants etc.

Water restriction notices are both issued and lifted on the advice of and in consultation with the HSE.

If you have received a water restriction notice and have any queries or concerns about your water supply, please call us on 1850 278 278.

When drinking water leaves a treatment plant it should be clear and colourless. However as water is carried through the water distribution network, it can sometimes disrupt sediment in watermains and become discoloured. e.g. disruption of sediment in cast iron mains can sometimes cause the water to have an orange or brown colour.

Irish Water operational staff undertake regular programmes to flush sediment from problematic areas of the network. However on occasion discoloured water can make it to the customer tap. Discoloured water can usually be cleared by running the cold water tap in the kitchen for a few minutes until the water runs clear.

Drinking water can sometimes appear cloudy or white and this can be due to different reasons including water hardness in an area or tiny air bubbles caused by trapped air in pressurised mains pipes. If your water looks cloudy or white, you can carry out a simple test to help determine what could be causing it. Fill a glass of water from the cold tap in the kitchen of your home and leave to stand for a few minutes.
If there are air bubbles in the water, they will rise and the cloudiness will start to disappear from the bottom of the glass upwards. If the water clears from the top of the glass downwards, the cloudiness or white colour may be due to limescale which is found in areas of hard water.

Hard water and air bubbles do not affect the quality of drinking water and are not harmful to humans.

If you have any concerns about discoloured water or water quality in your home, please call us on 1850 278 278.

Both taste and odour in drinking water are subjective characteristics, with some people being more sensitive to changes in how their drinking water tastes or smells.

The most common cause of taste and odour issues in drinking water is due to the addition of chlorine. Adding chlorine to drinking water is one of the most commonly used and proven methods of disinfecting public water supplies from microbiological contamination. Irish Water operators carefully controlled chlorine levels in drinking water supplies to ensure it is disinfected without causing negative taste or odour issues. However on occasion, changes in water quality require increased chlorine levels to ensure the treated water remains microbiologically clear to the end of the network. This can result in a more noticeable change in taste or odour in the drinking water.

A significant change in the taste or smell of drinking water can indicate a change treatment processes (e.g. more chlorine being added if necessary) a water treatment process failure, or the presence of organic matter or minerals that have been picked up as the water flows through the distribution network.

Other causes of taste and odour issues in drinking water can be due to algal blooms in the water source or the presence of organic matter and / or minerals that have been picked up as the water flows through the distribution network.

If you have any concerns about the taste or smell of your drinking water, you can call us on 1850 278 278.

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