Drinking water treatment process
In the UK, drinking water treatment involves a five-stage process that ensures the highest standards for our tap water.
1. Water Collection
All tap water starts as rainwater. This water is taken from the rivers, streams, and ground that it lands on, and pumped into a water treatment system where it continues its purification process. As our water comes from different sources and has filteed through the earth, 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 that 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 millimetre of rain over 150 days a year, and in some places, a lot more.
Reservoirs also help to start the water cleaning 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, a key step in filtration in water treatment. 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 during the water purification process.
- 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. This two-step process helps remove dirt, debris, and even some bacteria, making the water much cleaner before further treatment.
- Other chemical filtration methods include using carbon, ion exchange, and ozone.
5. Bacterial Removal
The final treatment in the water cleaning process 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.
Why does the water treatment process differ across communities?
Water differs across the country depending on where it naturally falls. This is why the water treatment process can vary from one community to another. Water sourced from rivers, lakes or reservoirs often needs more intensive treatment than groundwater, as it’s more exposed to surface-level contaminants like sediment, bacteria, and pollutants. In some areas, extra steps are needed to remove specific substances such as nitrates or even naturally occurring radioactive particles. Local water providers carefully tailor the treatment process based on the unique makeup of the source water, ensuring it’s safe and clean by the time it reaches your tap.
