JUST INSIDE the Co Kildare border with Co Wicklow, a tourist pulls into a lay-by during a break between April showers to take in the beauty of the Blessington lakes. He takes a few photographs and goes on his way, having captured a piece of Ireland’s natural heritage.
Except the image he has on his camera is not a lake, nor is it strictly speaking natural.
The picture is of the Poulaphouca reservoir constructed between 1939 and 1945 as a joint venture between the ESB and the then Dublin Corporation. It is the main source of drinking water for Dublin and also serves the surrounding counties which make up the greater Dublin region.
The reservoir stores enough water to last for between 120 and 180 days depending on rainfall, which rates well by international standards. However, it is the capacity to treat that water which determines whether homes and businesses have a reliable supply of drinking water.
Not far across the other side of the road from the lay-by is the Ballymore Eustace water treatment works. The plant is undergoing a major expansion, due for completion towards the end of next year. This will bring its capacity to produce water from 252 million litres a day, just 1 per cent above current customer usage, to 318 million litres a day.
The “raw” water is transported from the reservoir through massive pipes 1.6m in diameter (the same size through which Michael Caine drove a Mini in The Italian Job) to an intake tank called the manifold building. Here aluminium-sulphate, a coagulant, is added. This makes any solid particles in the water come together and takes the peaty colour off the water.
The water then flows into open- air sedimentation tanks from the bottom upwards. The sediment particles stick to lamellae plastic plates in the middle of the tank and the clearer water flows from the top of these tanks into open-air sand-filtration tanks.
The water flows down through the sand and a layer of gravel which traps the remaining particles, giving the water a final polish before it is taken indoors again through pipes at the bottom of the tank.
Inside three chemicals are added to the water: sodium-hypochlorite to disinfect it, lime to correct the pH and fluoride because the fluoridation is required by law.
The water is now ready to drink. The next step is to get it to the consumer.
More 1.6m pipes, or trunk mains, take the water to the Saggart storage reservoir, which feeds reservoirs at Stillorgan, for the south city and county areas, and Belgard for the north of the region. These two reservoirs send water to a network of service reservoirs around the city and county.
In Dublin city, the mains network is divided into six water supply zones. Water is piped from the service reservoirs through distribution mains into these zones, which are further divided into 200 district meter areas, which would cover approximately 1,500 homes each.
About 2,800 underground pipes carry the water in a web-like network through the city.
When the pipes reach the boundary of a property, they are either 6in (150mm) or 4in (100mm) in size, depending on the area and when mains were laid. From the stopcock at the boundary wall, pipes go underneath the house or garden at a size of half an inch or 19mm, depending on when the house was built.
The pipe is then divided into two, with one pipe going to a tank in the attic to be used for flushing toilets, feeding washing machines, showers etc. The second pipe, goes straight to the kitchen tap to provide drinking water.
