Here in the UK, we pretty much take it for granted that we can switch on the tap, and clean, healthy drinking water will emerge ready for consumption. But with less than 20 per cent of the world’s countries guaranteeing drinking safe tap water, it seems we are somewhat in the minority. How do our water companies ensure that all 64 million of us have access to drinking water every day, and how do they ensure that water is safe? Here’s what you need to know.

Where does tap water come from?

We all understand the basics of the water cycle; rain falls, water flows, sun warms and the water evaporates to make more rain. However, when we’re talking about crystal clear, bug free, safe drinking water for our domestic supply, there is a lot more to that journey that you’ve probably never stopped to think about.

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The source of your water will depend a lot on the water company who supplies you. Here are some examples:

Southern Water: Southern Water supply around four million customers around the South East of England with safe drinking water. 70 per cent of their supply comes from groundwater, largely from the chalk aquifer which spreads across the region. 23 per cent comes from rivers, and the remaining 7 per cent from surface reservoirs.

South West Water: South West Water supplies Devon, Cornwall and some parts of Dorset and Somerset. 90 per cent of their supply comes from reservoirs and rivers, with the rest coming from springs, wells and boreholes.

Northumbrian water: Northumbrian Water Supply 2.7 million customers in the north east of England. 99 per cent of their customers are supplied by large reservoirs around the region, apart from homes in Berwick and Fowberry who are supplied entirely from an aquifer in the Fell sandstone.

Thames Water: Thames Water Supply 8.8 million drinking water customers in and around the capital. 80 per cent of their supply comes from rivers, and the other 20 per cent from underground aquifers.

You can find out where your own water comes from by talking to your water supply company. In general, around the UK, mains water is a mixture of surface water from rivers and reservoirs and some from underground sources.

The treatment process

Knowing that a good deal of your water is coming directly from your local reservoir or river probably doesn’t fill you with confidence. At the best of times, these water bodies are often murky and full of leaves and debris. At the worst of times, they could contain dead animals, chemical runoff from neighbouring fields or other dangerous substances. They might be the water source, but they certainly aren’t ready for drinking.

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This means that after the water has been extracted from the source, your water supply company will need to put it through a series of treatment processes in order to make it safe to drink. This specific process is different depending on the company doing the treatment and the source of the water, but will usually include at least some of the following:

1. Screening: Water is passed through a screen or sieve to remove floating debris such as branches and leaves.
2. Ozonation: Some water companies treat drinking water with a chemically active form of oxygen known as ozone. As it passes through the water, it destroys any microorganisms and helps to oxidise metals.
3. Flocculation: In some treatment processes, water is ‘flocculated’, which involves the addition of a solution to encourage suspended particles to clump together. This can be particularly useful if the water is muddy, such as from a river, so that the mud can be more easily removed.
4. Filtering: Water companies will then filter the water to remove all impurities and unwanted elements. There are two main filters used by most water suppliers:

• Rapid gravity filtration: These filters pass the water through coarse sand, trapping floating particles as the liquid moves through.
• Slow sand filtration: Water then passes through dense sand, removing even the smallest remaining particles of contaminants and further clarifying the water.

5. Pesticide removal: Some water is treated with activated carbon filters to remove any pesticides which may have run off neighbouring fields into water sources.
6. Ultraviolet treatment: To further disinfect the water, a strong ultraviolet light is used which kills bacteria and viruses.
7. Regional corrections: In some areas, specific treatments are required to account for nuances in the local infrastructure. For example, in areas where there are lots of old lead pipes, phosphate can be added to reduce the risk of dissolution.
8. Chlorination: Finally, once the water is completely clarified, filtered and treated, a small amount of chlorine is added to keep the water safe right up to the tap.

Huge amounts of testing are done at every stage of the treatment process, with each individual water company carrying out millions of tests every year.

British tap water is amongst the safest in the world, and many companies claim that in tests, it beats bottled water for taste too. We’re lucky to be able to take our water supply for granted, so don’t waste it!