Marina Ventura’s Inside Water – the water treatment process

Where does our water come from?

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Do you ever wonder how the rain that falls from the sky ends up in your taps, or how it’s treated and gets to you?

Well, in-between it falling from the sky and coming out of your taps, there is a  whole process that involves hundreds  of treatment sites, miles of pipes and loads of tests.

Water Treatment

1 Collecting rain

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The water that comes out of the taps at your home, school and work starts off as rain.

This rainwater either flows into rivers and streams or filters through the earth to form ‘groundwater’, which is pumped to water treatment works where it goes through various treatment processes before being sent to you.

As water is taken from various rivers and ground water sources, the quality of it can be different, so the treatment process it goes through is tailored to make sure you get the best-quality water possible.

Did you know that water companies like Thames Water can only pump a certain amount of water out of rivers and underground sources so that they don’t harm the environment. This is one reason why we must all use water wisely.

2 Storage

Water 2At some of the larger water treatment sites, water is stored in reservoirs before it goes through the treatment process.  Water is stored in reservoirs for two reasons:

  • So that there is a store or reserve of water, so if it hasn’t rained for a while or the water companies can’t pump as much water from the rivers or groundwater sources, they have water available to put through the treatment process. Some reservoirs have enough water to last for 90 days.
  • Storing the water in reservoirs starts the natural clean-up process, as heavier particles settle to the bottom, meaning they don’t have to be taken out.

Did you know that Thames Water has 30 reservoirs, some of which are used by local communities for sailing, fishing, nature walks and bird watching?

3 Screening

Once water has been collected, it’s put through a screen to capture any branches or leaves. If left in the water they would almost certainly clog up the treatment process.

4 Removing particles

At some treatment sites, a solution is added to the water to make the particles bigger and easier to remove. This is called flocculation.

Then to make sure water is the purest possible, the water is then put through two more filters to remove invisible particles:

  • Rapid gravity filters – water is passed through a tank full of course sand. The sand traps particles as the water passes through.
  • Slow sand filters – water is then slowly filtered through large beds of much finer sand. This removes any remaining fine particles before the water goes for final treatment.

At some water treatment works, extra methods may be used to remove invisible and dissolved particles from the water, such as ozone, carbon and ion exchange. These methods create chemical reactions in the water and remove fine particles.

5 Final treatment

Once the water has been treated, the last thing done is to add a very small amount (less than one milligram per litre) of chlorine to it. This kills any remaining organisms or bacteria and keeps the water safe, right up until it reaches your tap

Did you know that water is tested at every stage of the treatment process by teams of samplers and scientists in laboratories?

6 Getting water to you

Following final treatment, the water leaves the treatment works and is stored in covered reservoirs. It is then pumped to you through our network of pipes and pumping stations.

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