Monday 22nd March is World Water Day. To mark this, here are some quick facts about our water supply: where it comes from, how much energy it takes to bring it to us, how long will it take for our water supply to be zero emissions, how healthy are our local streams and rivers.
It takes energy to supply water
The water industry is very efficient and mainly uses electricity. On average we each use about 140 litres/water per day [1] – and supplying this uses less than 0.2 kWh. That is about the same as boiling the kettle for two cups of tea. As more and more of our electricity supply comes from low carbon sources, the emissions from water supply (and boiling our kettles) also decrease.
Our water supply could be net zero by 2030
Treating our waste water generates methane and nitrous oxide which are powerful greenhouse gases. However, the methane can be collected and used for energy. This is a renewable energy source as it comes from biological processes. Water UK has published a 'routemap' for how the water industry can reach net zero carbon by 2030 [2].
Most people live in dry parts of the UK and water is an increasing concern
We transport electricity and gas around the country with little trouble but transporting water is harder because it is heavy. That means we rely on local water supplies for all our water. Some parts of the country are a lot wetter than others - but most of us live in the dry bits. Compare these two maps – rainfall on the left and population density (per sq km) on the right. The East of England is the driest area in the country. Water availability is an increasing concern.
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| Left - annual rainfall. Right, population density (per sq km) |
Nationally, 80% of our water comes from underground. In Cambridge: 100%
Nationally, 80% of our water comes from underground and only 20% from lakes and rivers [1]. Here in Cambridge, 100% of our water comes from underground. This is great, because underground water tends to be clean – it is has already been filtered by the rock as it percolates down – so it needs little treatment to make it safe for us to drink. Also, the aquifer acts as storage, and it does not lose water by evaporation in hot summers.
As we use more water, streams and rivers fed from the aquifers get less
However, aquifers supply rivers and streams too. The more we use, the less that feeds into these streams. On average, there is enough for all (at least there is at the moment), but if we have a drought, then the water level in the aquifers drop quickly. We use more water in hot dry weather, which makes the problem worse. Streams fed from the chalk aquifer where Cambridge gets its water are increasingly suffering low flows and drying up altogether when we get prolonged dry weather, which is not unusual! Low flow is the not the only threat to these vital natural habitats - but it is one of the gravest.
Only 10% of chalk streams in Cambridge are rated green for flow
The Wildlife Trust and and the Wild Trout Trust were commissioned by Cambridge Water and Cambridge City Council to assess the status of the chalk streams in this area [3]. This includes the River Cam. They looked at twenty sections from seventeen different streams and rated only two of them green for flow – meaning they have reliable flow. There were eight rated red – even though Cambridge Water supports some of them by pumping from the aquifer into the stream when the flow is very low. This helps but if groundwater levels are very low the water seeps quickly into the stream bed.
Watch our videos at the Earth Optimism Solutions Fair (starting 26th March)
Transition Cambridge asked Ruth Hawksley from the Wildlife Trusts about this, and also Councillor Katie Thornburrow. You can see the videos at Earth Optimism starting 26th March – look for Precious Water in the Solutions Fair (bathroom section). Also, check out the Transition Cambridge Water Project.
Can you use less water?
The average water consumption is 140 litres/person/day but it is not hard to use less. If you take care not to waste it, make sure you have water efficient toilets and showers and use a water butt for the garden you will probably find you use a third less than this. Try this water usage app to check.
[1] Discover Water
[2] Water UK Net Zero 2030 Routemap
[3] Greater Cambridge Chalk Streams Report (Wildlife Trusts and Wild Trout Trust for Cambridge City Council and Cambridge Water ) Dec 2020
To know how much water you actually use, take the figure given in cubic metres for the last 6 months from your last water bill (it is clearly shown there), then multiply by 1000 to give litres and divide by 182 (days in 6 months) and again divide by the number of people living in your house. This gives you 'litres per person per day' - it should be betweeen 100-150 litres).
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