Introduction

The Code for Sustainable Homes (“the Code”) is a national standard that aims to create homes that are more sustainable and reduce CO2 emissions.  The Code measures the sustainability of a home against nine categories including internal potable water consumption and external water use.

A pilot study has been carried out to monitor water consumption in dwellings built to Code specifications to compare it with values predicted by the Water Calculator in the Code, in order to assess whether the targets in the Code are practical and achievable.

Seven properties in which families lived normally were tested: five dwellings constructed to the standards of the Code and two to meet those of EcoHomes.  Water meters were fitted and the actual water use was measured for a period of between 6 and 12 months.

The study has shown that actual water consumptions in the dwellings on average exceeded the designed maximum water consumption targets set in the Code.  Although some improvements in water efficiency have been achieved, installing water efficient fittings and appliances as specified in the Code has only a limited effect on minimising water use.

Consumer behaviour and attitude play a substantial role in reducing water consumption.  Further research is needed to examine the impact of consumer behaviour and attitude on reducing water consumption through mitigation measures such as metering, awareness raising, and setting caps on water use.  A linear correlation between CO2 emissions and utility bills has been observed, which indicates that reduction in water consumption may help to reduce CO2 emissions, as well as lowering energy and water utility costs (this may not be the case where very low targets dictate the use of grey water recycling and/or rain water harvesting).

This study can also be used to assess the impact of Code water targets on reducing water consumption in new homes.

Aims

The main aims of the study were to monitor actual water consumption in Code dwellings and to compare this with the values predicted by the Water Calculator, in order to assess whether the Water Calculator method is practical, and whether the water consumption targets set in the Code are realistic and achievable.

The following key tasks were carried out:

• Test properties were located and actual water consumptions in these new homes were monitored.
• Protocols for retrofitting water meters in occupied dwellings and wireless telemetry for logging and transferring data were developed.
• The monitored water consumptions in each test dwelling were compared with the design water consumptions determined using the recently published Water Calculators.  These results were also compared with the maximum water targets specified for the relevant Code Level to assess compliance within the Code.
• Energy use and CO2 emissions associated with water consumption in the test homes were also determined. The purpose of this guide is to give best practice advice on wind- and weather-resistant installation of PV, solar thermal and microwind turbines on residential buildings. It includes examples of good and bad installation practice and detailed guidance on design for wind loading.

Key Findings

Key findings, albeit based on a small sample size, are as follows: 

• The average water consumption measured in the seven properties (109.57 litres/ person/day) was less than the current national average water consumption in existing UK homes (150 litres/person/day) and the target set in Building Regulations Part G (125 litres/person/day).  However, not all Code properties achieved the intended Code Level 4 target of 105 litres/person/day.  Two of the five Code dwellings significantly exceeded this maximum target value.
• On average, hot water consumption accounted for 32% of the total water consumption.
• With the exception of Property 6 where the water consumption pattern showed irregularity, the measured water consumption in the Code properties exceeded the values predicted using the May 2009 version of the Water Calculator by between 5% and 63% with a mean value of 28.6%.
• The water consumption values predicted using the October 2008 Water Calculator were higher than those predicted using the May 2009 version for each test property.
• Typical water consumption values per person per day were derived for the following appliances and fittings: WC (20.75 litres), bath (24.26 litres), shower (27.82 litres), wash basin (3.44 litres), kitchen tap (11.69 litres), dishwasher (4.75 litres) and washing machine (17.89 litres). These figures highlight that the greatest potential water savings can be achieved by reducing the amount of water used in WCs, baths and showers.
• Water use behaviours in all households monitored had a significant influence on the amount of water consumed, and the associated CO2 emissions, energy consumption and utility bills.
• In at least one case there was evidence of occupants exhibiting water-use behaviour associated with practical limitations of low-flow taps: ie the practice of filling kettles and other kitchen utensils from bath taps.
• CO2 emissions and household utility bills associated with water use were found to be linearly correlated. Generally, for every pound the household paid for its water use (including water bill and energy bill for hot water), approximately 2 kg of CO2 was emitted.
• On average, CO2 emissions were about 0.9 kg/person/day and the total cost associated with water use was approximately 50 p/person/day when using an average metered energy tariff.

The results in this study consistently show disparity between calculated use for a given water fitting specification and the actual water consumption.  This difference can be attributed to the impact of user behaviour which the calculator would not realistically be able to account for accurately in every case.  Given that the specification of water efficient fittings can only go so far in reducing water consumption and may not on its own achieve the targets set out in the Code and Part G, this study recommends further research on how user behaviour can influence water consumption.

The Code

The Code for Sustainable Homes is the national standard for the sustainable design and construction of new homes, and was launched in 2006.  It aims to create homes that are more sustainable and have lower CO2 emissions than conventionally built homes.

The Code is mandatory for social housing and homes built on ex-public land, and is required by a large proportion of planning authorities for new build homes in England; it is also mandatory for all developments of five or more units in Wales.

The Code measures the sustainability of a home against nine design categories.  Water consumption is one of the categories and includes mandatory targets for internal water use. Three maximum water consumption target values for internal water use are specified for different Code Levels (Code Level 1 or 2: 120 litres/person/day; Code Level 3 or 4: 105 litres/person/day; and Code Level 5 or 6: 80 litres/person/day).

The Code uses the Water Efficiency Calculator for New Dwellings (known as the Water Calculator) to predict water use in a dwelling and credits are awarded to the water category accordingly.  Water efficient fittings, such as reduced volume baths and low flow-rate taps, lead to predicted lower water consumption and hence a higher number of credits. The 2009 version Water Calculator is also used for Regulation 17.5K of Building Regulations Approved Document Part G(known as Part G) which sets a water target of 125 litres/person/day.