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How is Water Treated?

This guide breaks down the water treatment process and answers some common questions.

How is Water Treated?

In the UK, there are very high standards of regulation for both drinking water and wastewater. This means that all of our water goes through an extensive treatment process, but many people do not know what goes into keeping our water clean.

Why is water treatment important?

All of our water comes from natural sources and a lot of UK domestic water is collected in reservoirs, which fill when it rains. Although water is vital for life, this doesn't mean that all water is of a drinkable standard.

Due to contaminants such as bacteria, pollution, and other materials, untreated water can be very dangerous and make people extremely sick. Before modern water treatment technologies were implemented, contaminated water was responsible for disease outbreaks in many major cities. In 1858, London suffered from The Great Stink because the Thames was so full of human waste and pollution that the hot weather made the city uninhabitable due to the smell and transmission of diseases like Cholera.

Modern water treatment processes are vital for human and environmental health, especially in metropolitan areas.

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Drinking water treatment process

In the UK, drinking water goes through a five-stage treatment process. This ensures the highest standards for all of our tap water.

1. Water Collection

All of our tap water starts at rainwater. Water is also taken from rivers, streams, and groundwater, which has filtered through the earth. As our water comes from different sources, there is a mix of quality and contaminants. Therefore, it all goes through the entire treatment process.

2. Water Storage

90% of our water is stored in 570 reservoirs across the UK. These are man-made lakes and are used for water storage for drinking supply, hydropower production, and other water uses. Most of the water is pumped in from other sources like rivers and groundwater, but reservoirs also catch a lot of rainwater. This works well in the UK, as we get at least one millimeter of rain over 150 days a year, and in some places, a lot more.

Reservoirs also help to start the treatment process as there is no tide or current, so heavier debris sinks to the bottom and can be more easily separated.

3. Water Screening

Next, the water is screened. This means that large objects and debris are filtered out before they can clog the drains of the water treatment plant. These screens remove material like branches, leaves, and large grain sediment.

4. Particle Removal

At this stage, smaller particles that are invisible or dissolved in the water are removed. There are a variety of ways of doing this.

  • Flocculation: This is where a chemical solution is added to the water, which binds with tiny particles and makes them float, so they are easier to filter out.
  • Sand filtration: The water is run through sands with different coarsenesses. First, quickly through a larger grain trap, and then slowly through finer sand
  • Other chemical filtration methods include using carbon, ion exchange, and ozone.

5. Bacterial Removal

The final treatment is ensuring that any remaining bacteria and other unwanted contaminants are removed from the water supply. This is when chemicals like chlorine are added.

Chlorine is an essential element in the water treatment and sanitation process. It is a highly effective disinfectant that kills harmful bacteria and ensures that water stays safe during its journey to our taps. Sometimes water can smell or taste strongly of chlorine, but this does not mean that there is anything wrong with your water. There are a few reasons why your water might sometimes smell more strongly of chlorine:

  • Proximity to the water treatment plant. The chlorine dissipates over time, so if you live close by, you'll get the freshest water and that might smell more strongly.
  • It may be more noticeable in cold water as that holds chlorine for longer.
  • Water use peaks in the early morning and evening, which means it is pumped out from the treatment plant quicker and can retain a chlorine taste.

Water treatment plants typically use less than one milligram of chlorine per litre, which is far less than swimming pools (these can have between 1-5mg per litre). There are no health warnings related to this amount of chlorine, but if you are worried about the smell or taste of your water, you can contact your local authority.

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Wastewater treatment process

Wastewater refers to any water that is used and drained away such as in sinks, toilets, showers, and household appliances, and collected in street drains. This is all led back to a sewage treatment plant, where it is cleaned in a similar process to above, ready to be returned to rivers and the ocean.

As well as strict regulations around water that is used for human consumption, water that we return must be of a similarly high standard to protect the environment.

One of the big differences between water treatment and sewage treatment is the removal of human waste, otherwise known as "sludge". Most of this sludge is used in agricultural fertilisers, but a lot of it is used as a renewable energy source. In 2019, Thames Water self-generated 23% of its energy needs using sludge.

Treating water mains

A lot of the UK's water supply system was built during the Victorian era and there is currently nearly 100,000km of water mains and sewage pipes. Maintaining the health of these water pipes and delivery systems is just as vital to ensuring that water that was diligently cleaned at a treatment plant is not contaminated on its journey to your taps.

Although the water that leaves the treatment plant has chlorine in it that should help disinfect it, there is still the possibility that pipes may become contaminated if they have a weak spot or burst. However, the water mains are carefully monitored for any issues and regularly flushed through. This ensures that any sediment or debris is removed, as well as iron build-up, which may cause your water to have a metallic taste.

While UK water is clean and safe to drink because of the water treatment process, sometimes there may still be components that affect the taste. If you live in a hard water area or near a water treatment plant, then using a BRITA filter at home can help reduce limescale and any residual odours.

If you are concerned about the quality of your tap water, do not hesitate to contact your local authority.

If you would like to talk more, contact us. We're here to help!

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