Water efficient homes & drainage
Sustainability expert Nigel Griffiths reveals what you need to know to get your water usage in line with other eco elements of your home building project
Sustainability expert Nigel Griffiths gives the low-down on how to reduce consumption and save money on bills
With so much focus on energy efficiency and reducing the cost of heating and electricity bills, it can be easy to forget our homes and buildings also cause other environmental impacts. Water usage and drainage are both important issues, but their effects can vary depending on location.
For example, in the south east of England there’s a high concentration of people and a correspondingly high water demand, yet rainfall is the lowest in the UK – a situation that can even constrain development to some degree. By contrast, in the south west there’s plenty of rain but flooding is a regular problem, which makes sustainable drainage an essential part of any project. The point is that sustainability is a relative term. So exactly what you need to address on your project depends on where you are building and what you are trying to achieve.
Sometimes I hear people say that water is the new energy, implying it’s something else we should all start to get worried about. There’s a danger here, though. We live in a very temperate climate and anyone who’s spent more than a month in the British Isles knows that we’re not short of water. We rely on having sufficient storage and effective distribution of a mains supply – but there’s much we can do on an individual impact to reduce the impact of water and drainage issues in both new and existing buildings.
Water demand
Water use of course varies from one household to another. An often quoted figure is that the average person uses
150 litres (L) of water per day. For larger households, this figure drops as more services (dishwasher etc) are shared.
Plenty of free calculators are available online to help you work out your daily/weekly/annual use – but the pie chart on the opposite page, supplied by the Energy Saving Trust, gives a typical breakdown of yearly usage. Households with a water meter tend to consume less as there’s a direct connection between volume of water used and the bills.
There are various ways you can achieve savings. For instance, you could switch some appliances to more efficient modern versions, or make changes to your habits and lifestyle. Sometimes, households manage a combination of the two approaches.
It’s clear from the chart that over half of total water use in the average household is accounted for in the bathroom,
so this is the place to start when looking for savings in water use. But first things first – before you buy new loos and smart showering products, always make sure you fix any leaks. A dripping tap or cistern overflow can waste a surprising amount of water. There’s plenty more you can do, of course. Here are some of the top options:
1 Water-efficient toilets
Older single-flush WCS use 9L of water or more every time you pull the handle. Most modern WCS are dual-flush, and use either 6L or 3L/4L depending on which option you select. Some super-efficient versions can get this down to 4L/2L. If you still have an old cistern, then placing a displacement device inside is one option to reduce the volume.
It’s worth being aware that, as soon as the flush commences, water starts to re-enter the cistern. This means that actual volume used can exceed the stated amount. One way to avoid this is to install a delayed-action inlet valve, which means the cistern will only start to refill once the outlet valve closes. Over time, this builds to quite a significant saving.
The other thing to be aware of is people often throw tissue into the WC, which could easily be disposed of in the bin instead (or your stove/fire). This creates a tendency to flush the loo when it’s not really necessary, just to clear tissue from the pan. So just keep a bin handy! 2 Bathing & showering
Conventional wisdom has it that showers use less water than baths – but it isn’t necessarily so. Shower water consumption is a function of the power of the appliance and how long you spend in it. So a five-minute cleanse at 6L/min will use 30L; whereas a 10-minute power shower at 15L/min will use 150L. By contrast, a bath might use anything from 60L upwards – but there’s no time limit on how long you can soak for. Share a bath with a friend and water use per person is halved, of course, although it’s fair to say that’s not everyone’s cup of tea.
Low-flow devices typically run at 6-8L/min and increase the feeling of power by introducing air into the head. Another thing that works well is a shower timer, which encourages behaviour change. This can be particularly useful where there’s competition for the bathroom in the mornings, plus it’s much cheaper than buying a low-flow head. For new builds or major renovations, consider a shower with a digital timer.
Bear in mind that any savings on these activities will not only reduce your water bills, but can also save on energy – as it costs money to produce hot water. Unless you prefer a cold shower, that is.
3 Appliances
Washing machines and dishwashers have become more water-efficient in recent years. This is due to a strong drive to reduce their energy use – and as energy is mostly needed for heating water, so the volume of liquid used has also fallen. As long as appliances are relatively new, they should be pretty efficient. The best way to save water here is simply to wash things less often – but again, this is a lifestyle decision.
4 Rainwater harvesting
Rainfall can be harvested, safely stored and used for tasks such as flushing WCS. These systems aren’t cheap (expect to pay in the region of £2,500 for a typical setup) so you
need to be saving quite a lot of water to justify the installation on cost grounds. Check your utility provider’s water usage calculator and the price per m3 to do the sums on whether it might work for you.
Outside of the pure mathematics, instinctively it feels wrong to use drinking-quality water to flush away waste, when all the while every time it rains on our houses this potential resource is going straight into the drains.
Some of you may be considering grey water systems to recycle the waste from sinks, showers and baths. However, it’s worth noting that these are much more complex than rainwater harvesting setups – so the environmental impact of installing them is higher.
5 Water use in the garden
The first thing that leaps to mind for most people when it comes to reducing consumption in the garden is water butts. These can certainly help, but the majority of outdoor water use is for lawns – and it’s when a hosepipe is left on for a long time that the highest wastage occurs. Lawns will turn brown in a drought, but they don’t die and they’ll soon green up again when it rains; so ask yourself whether you really need to keep that grass pristine.
In fact, once established, most plants will survive without artificial watering. And in general, vegetable beds and hanging baskets are best watered by hand – which means the actual usage should be very low.
Sustainable drainage
The supply of water for daily use around the home is only half the story; it also needs to be taken away from our properties. Most systems that connect to the public drainage system are combined, which means sewage (including waste from baths and sinks) and rainfall (surface water) get discharged into the same pipework.
Surface water drainage is a growing issue for two principal reasons. The first is that the frequency of heavy downpours appears to be increasing as a result of climate change. Secondly, the development of both housing and commercial sites reduces the natural percolation of rainfall into the ground. Instead, it is conveyed directly into the drainage system, which can then become overloaded. Ultimately, these factors can increase the risk of flooding.
The best way to address these problems is through the use of sustainable drainage systems (SUDS). The two main techniques available for domestic purposes are:
1 Use of permeable surfacing materials wherever possible. These can be very simple options such as gravel, or more sophisticated products like permeable block paving. My personal favourite for use in parking areas is Buildbase Civils’ Ecoblock, a mesh made from recycled materials that can stabilize flat or sloping ground and can be filled with gravel or grass. 2 Holding water on site and releasing it slowly into the drainage system after the rain has ceased (known as attenuation). This can via be a pond or simply a swale (low tract of land) that has a small outlet; or via special SUDS geocellular systems such as Wavin’s Aquacell or Brett Martin’s Stormcrates. Note that people sometimes assume that rainwater harvesting or garden water butts can be used as a form of attenuation, but in reality the beneficial effect of these is minimal if heavy rain arrives. In terms of waste water, if you’re self building and your site can’t be cost-effectively connected to mains drainage, then you’ll probably be looking at septic tanks or a reed bed system to handle sewerage. Properly designed, reed beds can be so effective that the eventual run-off is drinking quality water; while the ponds themselves are an ecological asset. Another solution for sites that have no foul sewer access, especially if there are drainage problems such as heavy clay soils, is to install a composting toilet – although this approach is perhaps still the preserve of the deep green developer.