Water Treatment

How is water collected for us to use?

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. Do you know where the water comes from?

Scottish Water takes water from natural lochs like Loch Lomond, from underground lakes and from man-made lochs called reservoirs.

Reservoirs
Most of the water we use is collected and stored in man-made lochs called reservoirs. Most rain falls in hilly areas, so this is where most reservoirs are built.

We make reservoirs by building a dam across the upper part of the river. The water then collects behind the dam to make a huge loch. That means that even if it does not rain for several weeks, there will still be enough water for people to use.

A dam is made of very strong, thick concrete to hold back the huge amount of water. We can control how much water flows through the dam by opening and closing valves.

Water from rivers and lochs carries small bits of grit, dirt, plants and even tiny bugs down from the hills. Some of the grit and dirt sinks to the bottom of the deep reservoir as silt. The rest must be taken out at the water treatment works.

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 five different ways.

1. Screening - Leaves, twigs and any large debris are
   removed by screens.
2. Clarification - Mud and silt are removed. Alum (aluminium sulphate) and lime (calcium hydroxide) are added to make them group together to make sludge. This is taken away to a landfill site where it turns back into mud.
3. Filtration - Most treatment works have to filter their water. A special sand filter removes the last tiny bits of grit and any remaining colour.
4. Disinfection - The water now looks clean but may still contain bad bugs called bacteria. A small amount of the chemical chlorine is added to kill the bacteria (just like in the swimming baths).
5. pH correction - The water is still too acid to drink, so we must also add lime (calcium hydroxide) tomake the water less acidic and less corrosive to metal pipes. The water is now ready to drink.

How does clean water get to our homes?
The treated water is stored in large tanks and man-made lakes called service reservoirs.

Clean water is taken from the service reservoir through large pipes called water mains that are buried underground.

There is a water main under the road outside your house and the water in your tap comes through a pipe from that water main.

A stopcock in the house, or sometimes in the garden, can be opened or closed to turn the supply to your house on or off. It's a bit like a big tap.

Why don't you ask your mum or dad to show you where the stopcock is in your home?