The water cycle

Water is one of nature's greatest gifts. It falls from the sky as rain before finding its way into rivers or sinking into the ground. Eventually it returns to the sea, where it evaporates, forming rain-clouds and the whole cycle starts again.

Boy in the rain

The water cycle is very important to us here at Yorkshire Water, as it enables us to provide two million homes and businesses in Yorkshire with fresh drinking water every day. Find out more about how we make water work for you.

How we collect water

Considering the water cycle is truly a cycle, there's no real starting point, but if we had to pick somewhere to begin our exciting journey we'd probably say the sun.

Before we can extract the water from rivers, reservoirs and boreholes there are three main steps in the cycle - evaporation, condensation and precipitation:

Evaporation

The sun heats up the water from the oceans where it evaporates and rises into the air as water vapour. The vapour then rises into the earth's atmosphere, along with water transpired from plants and evaporation from the soil. Ask your pupils to think about what happens to a puddle when the sun comes out.

Condensation

As the water vapour rises, the colder temperatures cool the vapour so that it condenses to form water droplets in clouds. Clouds are formed when water droplets and pieces of dust join together in the atmosphere. If it's warm outside ask your pupils to think about why water forms on the outside of a glass when you pour cold water into it. If it's a cold day you could always ask them why water droplets appear on the inside of the window.

Precipitation

As the water vapour condenses the air can't hold it anymore so it falls back to earth as rain, sleet, snow or hail. The word precipitation comes from Latin and means "falling". Try asking your pupils to remember the name of this process the next time it rains.

Water treatment

A lot goes on at our water treatment works to make your water safe for drinking. The extent of the treatment varies depending on where we collect the water from - if it's from a borehole the water usually only requires minimal treatment, if it's from lowland river sources and upland reservoirs it will go through a tougher treatment process.

When water reaches our works it will normally go through the following stages to remove the "baddies":

Screening

The water passes through a huge metal strainer to remove debris like leaves and twigs.

Flocculation

Approved chemicals are added to act like a magnet for smaller impurities like dirt, natural colour and bacteria. The chemicals form a sort of jelly called floc.

We've developed an interactive guide to water treatment including cool sound effects and animations. Pupils can follow a gang of baddies on their doomed journey through the water treatment works.

Clarification

The floc has to be taken out of the water, so air is bubbled through the tanks to make the floc float to the surface to form a blanket, where it is scraped off. This process is called Dissolved Air Flotation or DAF for short. At some works that don't have DAF, the floc instead sinks to the bottom of the tanks and is taken away - this process is called sedimentation.

Filtration

The clarified water is passed through filters filled with layers of sand and gravel to remove any final traces of the floc and metals such as iron and manganese. These filters are cleaned regularly, every one to two days.

Ozonation

Ozone is a gas which is a powerful oxidant and is used at a few of our water treatment works. It is bubbled through the water to remove any traces of pesticides or similar compounds.

Granular Activated Carbon

Granular Activate Carbon is used in filter beds to remove the by-products of ozonation, as well as traces of any other substances which may also be found in the water.

Chlorination

Chlorine is then added to the water. This kills off any microbes that may still be present. A small amount of chlorine is left in the water as it travels to your home to ensure the water at your tap is of the highest possible quality.

We've only given you the basics of water treatment here. If you'd like to know more about how you can include this subject in your lesson plans, download our Science Pack - there are exciting water facts and fun, interactive experiments.

Water distribution

Having removed the "baddies" from the water we've collected it's now ready to be delivered to the homes, businesses and schools across Yorkshire.

We do this using our Yorkshire Grid which allows us to transfer water from one part of the region to another depending on where it's needed most. This means that, come rain or shine and wherever you are in Yorkshire, you can be assured that your water will always be on tap.

The grid also means that that the water your pupils drink at school has not necessarily come from the nearest source, it may have travelled several miles before it reaches them. Think of it like one giant water vending machine that never runs out of their favourite drink!

Collecting waste water

We have a network of around 20,000 miles of underground pipes, collecting the raw sewage from the region's homes, liquid waste from industry, and rainwater that falls on roofs and roads. After water's been used, it enters a waste pipe, travels into a drain, then into a sewer pipe that joins others to form something we call a trunk sewer.

Eventually it reaches one of over 600 waste water treatment works across the region where we improve the water before putting it back into the environment.

Treating wastewater

At our treatment works the wastewater goes through six key stages before it's good enough to be released into rivers and the sea:

1. Screening

We remove debris and large objects such as wood, rags, paper and plastics by passing the waste water through specially designed metal grids called screens.

2. Primary treatment

Sewage is transferred into large tanks called settlement tanks where most of the remaining solids sink to the bottom forming sewage sludge. The sludge can either be composted to improve soil quality, burned in an incinerator or digested by special bacteria to produce gas which can be burned to generate electricity - poo power as we like to call it.

Discover more about poopower in the classroom - download our guide to how human waste can help generate electricity. Key stages two and three.

3. Secondary treatment - stage one

The liquid sewage flows on to stage three which involves biological treatment. Here, the sewage is trickled over filters of stone containing billions of "goodie" micro-organisms which feed on the "baddies" and remove any organic pollutants.

4. Secondary treatment - stage two

Sometimes the sewage is mixed with the micro-organisms in a tank.  Oxygen is bubbled into the tank so that the "goodies" can breathe and go to work.

5. Final treatment

Finally, the sewage enters our settlement tanks where any remaining micro-organisms and sludge sink to the bottom. At coastal sites we also zap the waste water with ultra-violet light to kill of any surviving bacteria.

Returning water to local rivers and sea

It's important for our environment that the water we use is returned safely to the rivers and the sea. Many of our rivers are cleaner now than since the industrial revolution over 100 years ago. This is because we've been hard at work updating and modernising many of our waste water treatment plants in the region.

We also play a massive part in improving Yorkshire's coastal bathing waters thanks to a multimillion-pound investment in our waste water treatment in these areas.

To see how we're encouraging biodiversity and putting rivers back at the heart of communities in Yorkshire visit our Biodiversity page.

If you'd like to learn more about how we're helping keep Yorkshire's coastal waters clean, take a trip to the seaside.