Sustainability: Water efficiency

01 / When do you get your money back?

The forecasters have predicted that summer 2009 could be long and hot, and maybe even dry! In advance of the usual drought warnings and hosepipe bans, this article analyses the financial paybacks presented by water efficiency measures for a range of building types.

The article assumes that consumers are metered. Clearly, many domestic consumers are still not; however, legislation is slowly evolving to promote compulsory metering. The primary argument for this is that metering enables the consumer to monitor water use and consequently, better control (that is, reduce) their consumption.

In addition, following amendments to Part G of Building Regulations, from October 2009, all new homes will have to meet a water efficiency standard of 125 litres of water per person per day.

The main considerations that influence payback are listed below.

02 / Tariffs

Consumer tariffs are determined by the following key points.

Which water company is providing the water

All water companies are regulated by Ofwat; however the tariffs charged vary. The three key issues influencing them are the availability of water in the area, the relative density of the population being served compared with the infrastructure being provided (water companies serving higher density areas are typically able to charge less) and also the nature of sewage treatment needed. For example, those companies supporting areas with extensive spans of coastline are obliged to invest in more advanced sewage treatment works to comply with European legislation and so they typically charge consumers more.

How water charges are applied

Domestic consumers (when metered) are charged by the volume of potable water they consume. Water companies assume that all supplied water will then drain to foul or surface water drains and therefore do not charge two different rates. This assumption is broadly accurate unless potable water is being used for garden irrigation.

Charges to non-household customers typically vary according to the volume of potable water that the consumer uses and the volume of wastewater or trade effluent that the consumer discharges to foul sewage, surface water drainage and highway drainage.

Water charges vary (approximately) from £1.50 to £4 per cubic metre (1,000 litres).

Lastly, the amount consumed is also relevant, as typically, larger consumers are charged less per unit of water/wastewater.

03 / Water use patterns

The water consumption patterns of the end user influence the payback of each water efficiency measure. Variable consumption patterns are shown in the table, demonstrating payback periods of between 1 and 183 years. For example, in the case of offices, each toilet is used more times each day than in the home; therefore the payback period of investing in a water-efficient toilet is reduced.

(See table 1)

04 / Methodology

The three case studies considered are:

A Domestic consumer
B Office consumer
C Acute hospital consumer

Water savings presented are per item (per toilet or shower) rather than per person or per m2/whole building. Costs and payback periods are denoted for both new-build installation, and refurbishments. In the case of new build application, capital costs presented are those for the extra over costs (the difference between the cost of a regular tap and a water efficient tap); whereas refurbishment costs are whole item costs. Assumptions have been made regarding use patterns for each item; assumptions are clearly noted for ease of comprehension. The paybacks allow for both potable water savings and also discharges to foul sewer savings. Tariffs can vary significantly for discharges to foul sewer; therefore a consistent tariff equal to that of the water cost has been applied. All paybacks are presented as simple paybacks, i.e. without discounting the future benefits of water savings/operational expenditure.

05 / Conclusion

Clearly there are some quick wins in all three of the case studies, notably with water-efficient showers and taps in new-build and refurbished buildings, and replacement toilets in existing buildings.

It should also be noted that low-cost items such as domestic water butts, which do not present a favourable economic payback, do present clear environmental savings: gardens do not benefit any more from the application of treated potable water than untreated rainwater.

A / Case Study: Domestic consumers

As was said in section one, Part G of the Building Regulations requires new homes to consume no more than 125 litres of water per person per day.

How developers and affordable housing providers choose to meet this target will be discretionary, which means that they can adopt whichever combination of water consuming goods presents best value to the end consumer within the 125 litre limit. However, 6/4 dual-flush toilets have been the industry standard for some time. Consequently, the toilet comparison listed overleaf assumes the replacement of an existing toilet in an older home.

Showers, taps and bath efficiency measures can be applied to new and existing homes. However, rainwater or greywater measures can usually only be applied to new homes. Water-efficient white goods have not been included as most are water-efficient.

Water prices have been taken from Water and sewerage charges 2007-08 report (Ofwat 2007).

(See tables 2 & 3)

B / Case study: Office consumers

The majority of water use in offices is in bathrooms. Many water efficiency measures are now commonplace in new office schemes. However, new build represents a very low percentage of total office stock.

Showers and taps efficiency measures can be applied to both new and existing offices, but the toilet comparison listed below assumes replacement of an existing toilet in an older office building. The rainwater harvesting option can only practicably be applied to a new office. Greywater reuse is typically not appropriate for office application as insufficient greywater is generated relative to the volumes required for toilet/urinal flushing.

(See tables 4 & 5)

C / Case study: Hospital consumers

Hospitals use very large volumes of water. Toilet, tap and shower efficiency measures can be applied to both new and existing hospitals. The rainwater harvesting option can only practicably be applied to a new hospital. The capital cost of rainwater harvesting is typically higher in hospitals than offices as hospitals have many more toilets than offices and consequently the distribution pipework is more dispersed. Although hospitals generate high volumes of greywater, reuse is typically not considered appropriate as it does not align with best practice infection control measures.

The toilet option shown assumes a toilet in a publicly accessible area (that is, subject to high use patterns) rather than an en-suite bathroom attached to a hospital bed.

(See tables 6 & 7)