The Building Conservation Directory 2020

146 T H E B U I L D I N G C O N S E R VAT I O N D I R E C T O R Y 2 0 2 0 C AT H E D R A L C O MM U N I C AT I O N S Grey water systems Grey water must often be treated more thoroughly than rainwater because the presence of dirt, soaps and other substances can support biological growth leading to odour, discolouration and pathogens. Immediate direct re-use, for example watering the garden with used bath water, requires no special equipment or installations but is inconvenient. Some systems minimise the necessary treatment by storing grey water for only a short period. This can involve dedicated control systems that purge the storage if for example a family goes on holiday. The other option is to treat water more thoroughly by biological, mechanical or chemical means so that it can be safely stored before re-use, but this is unusual. The storage tanks can be smaller because they are not vulnerable to dry spells of weather, and supply will track demand fairly closely. A day’s supply might be sufficient storage in a grey system, whereas a rainwater system might need a few weeks’ worth or water in reserve. However, these treatment systems can be quite extensive, and it usually still has to be pumped back to the point of use. A key consideration for both types of system is that it is often necessary to almost double the extent of the cold water pipework, because many areas need both potable and rain or grey water supplies. If an existing building is being converted or thoroughly re-plumbed then it might make sense to fit the extra pipework, but generally it is not feasible to open up an SUSTAINABLE WASTE WATER SYSTEMS TOBY CAMBRAY T  RADITIONALLY CONSTRUCTED buildings are difficult to insulate to the levels expected of modern houses without damaging them. On the one hand there is a risk of interstitial condensation saturating the fabric, causing mould growth and even greater heat loss. On the other there is the impact that changes to the fabric can have on character and significance, particularly where the building is listed. So we tend to look for other methods of increasing their efficiency. Waste water is one of these. Whenever we pull the plug from the bath, empty the washing up bowl or take a shower, we literally pour valuable resources down the drain. As well as the water itself, significant amounts of heat energy in warm water is lost. This raises the question: what can be done to reduce, re-use and recycle these resources? GREY WATER AND RAINWATER RECYCLING The Environment Agency (EA) regularly publishes a map that indicates the UK’s level of water stress, which compares the inputs from rain with the outputs from abstraction in each body of water. Much of the UK is classified as low stress, thanks at least in part to its infrastructure which transports water from reservoirs to the cities; however, it still has significant areas of moderate and high water stress that may increase with the growing population. Additionally, the uncertainties around the effects of climate change are likely to lead to more extreme weather, possibly making it harder to capture and store water. Water companies are constantly encouraging us to reduce our consumption, many of them giving away useful items such as shower flow regulators, and Part G of the building regulations places stringent design limits on water-use in new build homes. With all this in mind, it might seem sensible to re-use waste water from wash-hand basins, baths and showers, known as grey water, and to collect and utilise rainwater. Shades of grey Grey water is the effluent from handbasins, baths and showers which is not fit for drinking but is fine for flushing the toilet. Rainwater is similar, but is also used for laundry, watering the garden and washing the car. Black water is a polite term for the effluent discharged from WCs, and it usually includes water from kitchen sinks and dishwashers, which contain grease and food particles that make it difficult to re-use. Water straight from the mains, or that has been processed to specific legal standards, is called potable. In principle recycling water is simple: store rain or grey water in a tank and feed the toilets and other facilities as and when. However, as with many topics in building, the devil is in the detail. Rainwater systems All systems need some sort of treatment: for most rainwater systems this can be as simple as a filter to separate out leaves and other debris. Rainwater tanks are sized to last through dry spells, but the length of the dry spell to design for is debateable. 3,000L for a single three-bedroom house is typical, or a 1,800mm by 1,700mm cylindrical vessel. After the bulk storage tank, there are two distribution options often referred to as direct and indirect. Direct is the most common option for domestic properties and involves pumping the water out of the bulk storage tank and, excepting a few valves and accessories, straight into the pipework that feeds the WCs and other appliances. Indirect systems pump water up to a smaller header tank which feeds the appliances by gravity. In both cases, an electric pump is essential, as is the additional pipework to carry the non-potable water this means the amount of cold water pipe work can nearly double. Occasionally a site will lend itself to a gravity only system, but this depends on all the draw-off points being lower than the bulk storage, which itself must be lower than the roof or collection area. Meeting climate-change targets requires retrofitting measures for existing and historic buildings, but some measures can be counter-productive