Future water use and greenhouse gas emissions

Paul Boughton

Saving water in the home can reduce greenhouse gas emissions and lead to lower energy and water bills, according to a new report from the UK’s Environment Agency (EA).
“The greenhouse gas implication of future water resources options” study analyses the carbon impact of water companies and also household water usage in the UK. The report outlines how different water supply schemes and options to help customers reduce water compare in terms of greenhouse gas emissions. It shows how the water industry and householders can significantly reduce these emissions through smarter energy and water use.

The findings from this report are also good news for household utility bills. In the face of rising energy prices, water metering alone could reduce customers’ water and energy bills by between £40 and £160 per year.

In 2006/07, the water industry produced five million tonnes of greenhouse gases. This means that the 23 companies making up the water industry were responsible for about 0.8 per cent of the annual UK greenhouse gas emissions.

In comparison, the use of hot water in homes for activities such as personal use, household washing, cooking and cleaning amounts to around 35 million tonnes of greenhouse gases per year. This is seven times as much as that emitted by the water industry and amounts to over 5.5 per cent of total UK emissions.

Paul Leinster, chief executive at the Environment Agency, said: "Looking across the life-cycle of water supply, household water use and sewage treatment, we calculated that for every million litres of water around seven tonnes of carbon dioxide is emitted. Of this total, 6.2 tonnes results from the use of water in our homes. Every day, the average household uses 350 litres of water and produces around 2.2kg of carbon dioxide through the use of hot water. Over a year this equates to the same level of emissions as produced by driving 2400 miles in an average family car.”

He added, "Increases in greenhouse gas emissions are contributing to climate change but simple measures, particularly those which reduce hot water use such as metering, spray taps and efficient showers, have the potential to save water and energy and reduce carbon. For example, moving to full water metering in England and Wales could reduce annual emissions by 1.1-1.6 million tonnes of carbon dioxide per year. This is the equivalent to around 340 000 to 490 000 (up to 2 per cent) fewer cars on the road each year out of a total of around 25 million."

Water companies are now required for the first time to include the cost of greenhouse gas emissions in their water resource management plans and to give details of annual emissions associated with their water supply activities.

"As we look to the future it is clear that both climate change and population growth are set to increase the pressures on our scarce water resources, particularly in the south east of England. By looking at the carbon cost of water management we can now understand which types of future options will increase our emissions further and those which will actually reduce our emissions.”

Summing up the report, Leinster concluded, “Using this work will enable us to adapt to the impact of climate change and at the same time prevent even greater future impacts by reducing our emissions now. This work clearly demonstrates that building new resource schemes such as desalination and new reservoirs will result in higher emissions whereas measures which help customers to reduce water use result in an overall reduction in emissions. To secure sustainable supplies of water we will need to implement the right balance of options to help customers manage their demand for water as well as consider some new water resource schemes. Our new report will enable ourselves, the water industry and other stakeholders to find the right combination for the future, helping us to maintain secure supplies for customers while also ensuring a lower carbon future. Getting it wrong will leave a legacy of carbon-intensive water management which will remain with us for decades to come."

A summary of results is shown in Table 1. These are average values, based on the EA’s high-level assessment. The range of life-cycle emissions associated with new supply schemes, in particular, is large. To select the lowest carbon solution requires a scheme-by-scheme assessment. The study has not considered the wider economic or environmental costs of implementing these options, nor the availability of water for abstraction.

A discussion of the results the assumptions involved, including the carbon costs of demand management combinations for new homes is available from the EA’s website, www.environment-agency.gov.uk

Table 1. Summary of future water resources options.

Emissions    Carbon cost
Demand management option(*)    KgCO2e/day/house    Pence/m3
Metering and tariffs    2.08    25
Smart metering    2.14    25
Conventional metering    2.20    26
Efficient showers    2.25    26
Spray taps    2.38    26
Water audits    2.36    27
Efficient baths    2.30    28
Low flush toilets    2.42    28
Current water ‘supply-use-disposal’ carbon cost    2.43    28
Community rainwater harvesting (retrofit)    2.56    34
Individual household rainwater harvesting (retrofit)    2.67    38
Community grey water reuse (retrofit)    2.59    39
Individual household grey water reuse (retrofit)    2.71    44
Emissions    Carbon cost
New supply option(*)    KgCO2e/day/house    Pence/m3
Current water ‘supply-use-disposal’ carbon cost    2.43    28
Direct ground water abstraction    2.46    29
Aquifer storage and recharge    2.47    29
River intake    2.48    30
Indirect effluent reuse    2.57    31
Reservoir    2.61    31
Desalination (brackish water)    2.91    34
Desalination (saline water)    3.77    44
* Figures are indicative for each option, and are not cumulative values. Source: UK Environment Agency.

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