Loch Katrine in the Trossachs has supplied the city of Glasgow with clean fresh drinking water for over a century and a half thanks to the work of the Victorian engineer John Frederick Bateman. When we have such an abundance of water there is little pressure to save water and you may be thought daft for even suggesting it but are there wider environmental benefits of reducing water consumption here?
The water that comes out of our tap has been treated and delivered to our home.
Treatment normally consists of allowing the water to gravitate through filters with the addition of various chemicals to remove suspended particles and pathogens such as cryptosporidium. As the water flows through the treatment process by gravity, no energy is required to move the water about but the filters do need to be reversed periodically to clean them and this requires energy to pump water back up the hill. The chemicals used also require energy to be produced and transported to the works, however the quantities are very low.
In Glasgow, like many other towns and cities, the water supply flows downhill from source to treatment works to consumers without need for pumping. Once the infrastructure is in place, there is very little energy used to deliver the water. This is why they typical carbon footprint of tap water in the UK is only 0.25g CO2e per litre. Based on the average 150l/day consumed in the UK, this is equivalent to driving 20 miles per year. Energy savings (and hence reductions in CO2 emissions) from saving a few litres of water around the home are trivial compared with a foreign holiday or driving a car. For example, the ten mile round trip to the garden centre to buy a water butt would generate as much carbon emissions as half a years water use: if the water butt reduces consumption by 10% it will take five years to pay back the carbon from fetching it from the shop before we start to pay back carbon from manufacturing and getting it to the shop!
However, a much more significant energy saving could be achieved if the water supplier, Scottish Water, reduced leakage rates. Treated water in Scotland was consumed as follows in 2009-10:
Domestic consumption 37%
Non-domestic consumption 22%
Leakage 38%Source: http://www.scotland.gov.uk/Publications/2012/06/4338/4
This is a big improvement on a few years earlier with the daily leakage being reduced from 1,100 million litres per day in 2005-6 to about 700 million litres per day in 2009-10, which equates to a saving of around twenty thousand tonnes CO2 per annum but there is still a long way to go.
There is clearly a financial cost to tackling leakage. The leakage reductions from 2005-2010 were the result of a £2.45 billion investment programme. With almost 48,000 kilometres of pipes in the distribution network the cost both financially and in carbon terms of digging up the ground and fixing leaks is high. Not only do we have the environmental impact of manufacturing the pipes and operating the plant to dig the hole and lay the pipes but we also have the inevitable increase in traffic congestion caused by the works. The savings from plugging the leak may take many years to pay back the cost of fixing it, in both financial and environmental terms, but in the long term it is a sound investment. A leakage rate of 10% or less has been achieved in other places.
Taking a slightly different approach, Scottish Water's new Glencorse Treatment Works features a hydro electric turbine which generates enough electricity from the incoming water to meet half of the needs of the works and they are considering installation of wind turbines at other works. While operating the treatment process with renewable energy does mitigate the impact of the leaks it is not a long term substitute for maintaining and repairing the distribution network.
Since the carbon savings from reducing domestic use of water are so small and the bigger problem of leakage is beyond our control should we bother trying to reduce our water use? Well, there are circumstances where saving water at home has a much bigger impact.
When we heat water the physics changes. Heating water is one of the largest components of our domestic energy use and any saving here is worthwhile. This is where a quick shower with a water reducing shower head beats a bath and boiling just the right amount for a cup of tea beats filling the kettle. It is not water saving that has the impact but rather heat saving therefore the method used to heat the water can have as big an influence on the energy used as the volume.
Manufacturing plastic bottles, transporting them to a spring or other water source (sometimes even a tap), filling the bottles, transporting them by lorry to the shops, possibly kept in a chiller, purchased, drunk, bottle disposed of and collected for landfill or recycling: a lot of work when there is a pipe with a tap already there. It has a carbon footprint approximately one thousand times that of tap water, not to mention the millions of bottles that end up in landfill sites each year. Avoiding bottled water makes a significant saving
The embodied water or water footprint of products is the amount of water that is used to make them rather than the amount of water physically contained in them. About two-thirds of the embodied water in goods and services consumed in the UK is imported, often from places with limited water resources. It can be difficult to tell which things have high embodied water and, if they do, how significant it is. Some products may have a lot of embodied water but originate in an area where water is plentiful, in which case it isn’t a big concern. In more arid areas can be much more of a problem, such as cotton produced in Uzbekistan and Kazakstan at the expense of the Aral Sea or roses grown in Kenya using limited water that could be use to grow food.
This is an area where we can save water and make a real difference but it is not easy. There is quite a bit of generic information about the types of products that tend to have high volumes of embodied water but limited information on specific products made in different parts of the world. More information can be found at http://www.waterfootprint.org
Scotsman article on Scottish Water’s leakage: http://www.scotsman.com/news/scottish-water-plugging-the-gaps-but-leaks-still-an-issue-1-1498259
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