How Water is Treated

Water Treatment

The water that is supplied to residents and businesses in Ireland comes from different sources, such as lakes, rivers, streams, springs and boreholes (wells). Depending on the quality of the source, the water that comes from your tap will almost certainly have to go through some form of treatment to make it safe for you to drink. All water supplies that are used for human consumption must meet certain standards, which have been laid down by the EU. They have to be free from micro-organisms, parasites and from any substances that may be a danger to public health if they are found in sufficient numbers or concentrations.

From Source to our Taps

Step 1

Water is taken from a source and in most cases stored in a reservoir. The source of water may be a river, a lake, groundwater taken from below, or a well for small supplies serving a small number of houses. For large supplies a river may be dammed creating an artificial lake. In Wicklow there are two such lakes. Damming the River Liffey formed the Blessington lakes. Near Roundwood we have the Vartry Reservoir where the River Vartry was dammed.

Step 2: Sedimentation

It is used to remove floating and dissolved particles. Water is pumped to a treatment plant where it passes through settlement tanks. To assist particles to settle out of the water, chemicals such as Alum are added to the water. Particles of dirt and minerals stick to the alum and as they clump together they become heavier than water and sink to the bottom. The water flows on to the next stage of treatment.

Step 3: Filtration

While sedimentation removes most of the dirt and particles some fine particles will manage to escape the sedimentation tanks. Filtration is used to capture these fine particles. For filtration of water we have learnt from nature and know that the best filters are sand and gravel. The water passes first of all through a layer of gravel and then a layer of finer sand. Small particles get trapped in the gravel and sand. Some filtration systems are so efficient that little or no chemical treatment is needed after this stage.

Step 4: Disinfection

When contamination is found which may lead to harmful bacteria entering our drinking water, the Council may issue a Boiling Notice.

This notice tells us to boil water for drinking until the problem is addressed and further tests show that there is no longer potential contamination. Sometimes, water is further treated with UV light to kill bacteria or treated to remove nutrients such as phosphorus.

Step 5: Storage

Clean water may be stored in storage towers or reservoirs to serve demand as needed in our community. Supplies will build up during times when we use little water such as during the night. Demand for water is particularly high in the morning and the evening. In each of our homes and buildings we have our own little storage tower for water. The tank up in the attic is the highest place to store our water ensuring a strong flow down into our taps. Water in the tank in the attic may get contaminated with some dirt over time so we should never use it for drinking water. Instead when we want to drink water from the tap we use a tap that is taking water directly from the main water pipe that is bringing the water into our home or other building. At home this will usually be the cold water tap in the kitchen.