Cutting water use also cuts carbon, says Agency

Demand management measures will help water companies and their customers save money and cut greenhouse gas emissions, says the Environment Agency. This may justify metering and special tariffs, even in areas not short of water.

An Environment Agency research project has shed light on the greenhouse gas implications of water companies’ plans to manage the demand for water and develop new water supplies.1 It finds that some ‘demand management’ measures - such as household metering and water efficiency audits - offer the best hope of reducing emissions. But new resource development and some water saving measures will add to the upward pressure on water industry greenhouse gas emissions.

The study aims to inform investment in new water supplies and demand management measures such as metering during the 2009 water industry price review. Its timing is good as water companies are obliged by regulator Ofwat to include the shadow price of carbon in their investment plans and will be joiing the government’s Carbon Reduction Commitment scheme in 2010.

The UK water industry released greenhouse gases equivalent to five million tonnes of carbon dioxide in 2006/07, the study reveals, or 0.8% of the UK total. The sector’s emissions are rising due to increasingly stringent environmental obligations that are raising its energy consumption (ENDS Report 401, pp 32-36 ).

But seven times the industry’s total emissions arise in the water cycle from domestic water heating (not including space heating) - that is 35MtCO2 e/yr and 5.5% of UK emissions.

For each million litres - or thousand tonnes - of water supplied, the study notes that seven tonnes of CO2 equivalent are emitted: 89% from ‘in home’ water heating. The remaining 11% consists of 7% from wastewater treatment, 2% from water treatment, 1.6% from water distribution and 0.4% from abstraction (see chart).

Reducing the demand for water will result in significant energy savings for companies and for householders, the Agency says.

Many water companies are under pressure to develop new water supplies, replacing existing sources that are being reduced by the Agency to protect wildlife sites, in line with the 1992 EU habitats Directive.

All new supply measures by companies raise energy use, the report reasons, but by varying amounts. Household water supply, use and disposal emits an average of 2.4 kg CO2 equivalent per household per day. But new desalination schemes would increase this by 20% or 55% depending on whether brackish or salt water was used. Even new reservoirs would increase emissions by an average of 0.2 kg CO2 e/household/day.

Surprisingly, some water-saving measures result in higher carbon emissions, suggesting they may only be worthwhile in cases of severe water stress. The study found retrofitted community rainwater harvesting and greywater reuse schemes increased household greenhouse gas emissions by 0.13kg and 0.16kg per day respectively.

However, metering and special tariffs could reduce water-related greenhouse emissions by over 14%, the study found, to below 2.1kg per household per day.

Trevor Bishop, the Agency’s head of water resources management, concluded: "Even in areas not considered to be water stressed, pursuing demand management measures should be examined in the light of the carbon benefits they bring. We believe that widespread implementation of these measures can offset or further reduce overall emissions, as well as reducing the need for some of these new supplies in the first place."