Cleaning waste water
Our sewerage systems collect wastewater from your homes and schools and carry it through a network of underground pipes to our treatment works. Here the effluent is cleaned and returned to the environment.
What is wastewater?
This is the water poured down the drain after washing dishes, taking a bath or flushing the toilet. In fact, wastewater includes all types of used water. The waste water contains a variety of substances, some dissolved and some in the form of solids which will float, sink or stay suspended in the water.
- Domestic water from baths, washing up, toilets etc.
- Industrial waste water from factories.
- Rainwater that runs off roofs, roads and paved areas.
Wastewater collection
Collecting this enormous amount of wastewater and getting it to a treatment works is a major engineering task requiring a vast network of sewers spreading out to virtually every home, office, shop, school and factory in the country.
In the region covered by Welsh Water alone, this amounts to approximately 36,000km of sewers and drains.
Sewage network types
Most of the UK has a combined sewerage system, meaning that both rainwater and wastewater (from toilets, bathrooms and kitchens) are carried in the same pipes to a sewage treatment works. Large parts of it was built over 120 years ago during the Victorian times and if we were designing a system now, we would do it very differently and have separate pipes for sewerage and rainwater. This is how new housing developments are designed.
Storm Overflows
During heavy rain stormst, more water goes into the older 'combined' systems that carry both rainwater and wastewater. These pipes weren't designed to hold all that water, so they have release points called Storm Overflows that let the extra water out safely.
Most of this water is rainwater — about 95%. It goes into waterbodies, which should already be in flood. If we didn’t have these overflow points, the pipes would fill up too much and sewage could flood streets or even cause toilets to overflow in homes.
Let's Stop The Block
Wet wipes (including those labelled as “flushable”), disposable nappies and sanitary products are the main items that cause problems in our sewers; but kitchen oil, fats and grease can also lead to major blockages. These items should not be disposed of down the drain. Around half of all sewer blockages are caused by the wrong things being flushed down the toilet or poured down the kitchen sink.
Welsh Water’s campaign called Let’s Stop the Block raises awareness about what can and cannot be flushed down toilets and put down drains.
Wastewater treatment
The purpose of wastewater treatment is to remove enough impurities from the wastewater to enable it to be returned safely to a river or the sea where it can again become part of the natural water cycle.
The process by which wastewater is cleaned is made up of be a series of stages including screening, settlement and use of microbes to remove suspended solids in the water. Full details can found in our detailed downloadable information sheets at the bottom of the page.
Turning Poo Into Power
It’s hard to believe that wastewater and sewage could be used to light our homes, we call this Poo Power!
Poo Power uses a biogas rich in methane which is removed from the treatment of wastewater and sewage to drive the turbines. The biogas, predominantly comprising of methane, is produced when bacteria feed on human and animal waste. This process is known as anaerobic digestion and it is a great way to produce green energy, as well as getting rid of waste and the micro-organisms that lurk in it. One of the simplest ways of describing anaerobic digestion is the ‘farting’ of millions of tiny bugs within the waste, which produces the biogas.
Positively, when the biogas is burnt for generating electricity far less carbon dioxide is released than when fossil fuels are burnt.