After the deluge?
A torrent of policy, regulations and standards for sustainability have poured down on the sector, but how have these impacted upon best practice in water effi ciency? A team of specialists at Hilson Moran give their view
E
ngineers are striving to reduce flow rates all the time, while ensuring sanitary and drainage systems function effectively, in a bid to meet the challenges posed by BREEAM, the Code for
Sustainable Homes (CSH) and the updated Part G of the Building Regulations. But despite engineers conducting extensive assessments of predicted water use and gaining post- occupancy water meter readings, it’s still difficult to know precisely what the population of a building will actually be and, therefore, exactly how much water is required. Water demand in a commercial offi ce building used
to be 40 litres per day per person, but this has reduced dramatically over the last 10 years and is now thought to be closer to 25 litres per person. Credits are awarded under BREEAM, for example, for water conservation by encouraging reductions in water use, the use of low water use fi ttings, and through the detection of leaks. But to make systems work at much lower fl ow rates, it
takes not just the right specifi cation of materials, but also the right communication with clients and end users. It’s also important at the design stage to ensure that the low fl ow rates being sought are refl ected in the architect’s specifi cations, to ensure the sanitary ware selected is compatible with the system’s design. If incompatible fi ttings are used, it can cause issues with water delivery. For example, the WC pan and cistern need to be
54 CIBSE Journal September 2010
designed and tested as a single unit to ensure the effective evacuation of the bowl and to minimise the need for the user having to carry out a second fl ush. The CSH is endeavouring to reduce the consumption
of water in the home from a previous average consumption of 135-150 litres per person per day to an aspiration of just 80 litres per person per day, in order to achieve Code levels fi ve and six. However, reducing the fl ow rates too stringently in showers, for example, could easily mean that people require a longer one to rinse off lather, so the anticipated water savings become rather self-defeating. Get it wrong in either environment and the occupants will soon be changing the fi ttings, post occupancy. Designers can’t afford to ignore what’s lurking
below ground either. They need to look at the entire installation, right down to the drainage level, to ensure that new sanitary ware won’t cause future problems. For instance, there is no distinction in BREEAM between old and new buildings in terms of water consumption requirements. However, retrofi tting modern low-fl ow fi ttings to work
with an old drainage system could cause serious issues. For example, older drainage systems that were designed to convey nine litres per WC fl ush can now be using just 4.5 litres today, causing solids to settle and increasing the risk of blockages, as well as changing the ratio of sludge to liquid in the effl uent that arrives at the water treatment works. To achieve the full three credits rating in BREEAM
Offi ces, engineers are obliged to incorporate rainwater harvesting and/or grey water recycling solutions into their design. However, this can be quite a challenge, especially in commercial buildings, which, generally speaking, have quite small roof areas relative to a building’s population. In reality, rainwater harvesting and grey water recycling can only deliver a small percentage of the water required by a multi-storey offi ce building.
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