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Water treatment


Water from lochs and rivers may look clean but it needs to be treated before it is safe to drink.  How is water collected for us to use? Girl under umbrella  It's simple to turn on the water tap and fill a cup with clean drinking water, but a lot of things have to be done before this can happen. First of all, water has to be taken out of the natural water cycle.

Reservoirs

Most of the water used today is collected and stored in man-made or natural lochs called reservoirs.  Rainfall is highest in hilly areas, so this is where most reservoirs are.

Reservoirs are made by building a dam across the upper part of the river. The water then collects and makes a huge loch. So, even if it does not rain for several weeks, there will still be water available.

The dam has to be made of very strong, thick concrete to hold back the huge amount of water behind it.  The amount of water flowing through the dam is controlled by opening and closing valves.

The Scottish Environment Protection Agency (SEPA) set minimum compensation flow rates from the dam to protect the environment such as fish, wildlife and plants downstream.The water in the reservoir needs to be cleaned before it is ready for us to drink. The river has carried lots of bits of grit and dirt down with the water. Some of this grit and dirt will sink to the bottom of the reservoir as silt. This happens because the water in the reservoir is deep and still. The rest is removed at the water treatment works which makes the water clean and safe to drink.

Underground lakes

Sometimes a reservoir forms naturally underground. Rainwater soaks into the ground and through the rock below. This can only happens where there are soft rocks like chalk and limestone. They soak up a lot of water. They are a bit like underground sponges.

The water then collects in a space between layers of rock. We call this an aquifer. We collect water from the aquifer by drilling boreholes in the rock and pumping the water out.

Why must water be treated?

Water from a river or well may look clean but it can contain harmful bacteria, rotting plants, minerals, natural or man-made chemicals, as well as dirt. Some of these things are harmful and even poisonous. Others just make the water taste bad.

At the water treatment works all the water is cleaned so that it tastes good and is safe to drink.

How is water treated?

Water from the reservoir is transferred to the water treatment works where it is treated.  Click here to see a typical example of the water treatment process (pdf).


June 2012 saw the official opening of Scottish Water’s Glencorse Water Treatment Works (WTW).  Click here to see the video about the Glencorse water project which provides a new treatment works to bring 175 million litres of clean, safe water per day to 450,000 people in Edinburgh.


How does clean water get to our homes?

When clean water leaves the water treatment works it travels through large pipes called water mains that are buried underground.

There is a water main under the road near your house and the water in your tap comes through a water supply pipe.  This pipe is controlled with a stop cock which is placed on the communication pipe.

A stop valve in the house or sometimes in the garage, can be opened or closed to allow you to turn the supply from the water main to your house on or off.  It’s a bit like turning a tap on or off.

 A diargram showing where Scottish Water is responsible for your pipes

 Your responsibility table