Reducing wastewater at home

Let’s fill our metaphorical bucket, dip in our mop and wring out a few home truths about water. We drink it, cook with it, and wash with it. But are we taking enough care of our water? Particularly since some parts of the world are predicted to become much drier through climate change. A recent paper in the journal Science estimates that up to a 5th of groundwater wells are at risk of running dry. So how can we tread a bit more lightly in the way we use water in our homes in future? Chris Smith spoke to Sarah Ward from the West Country Rivers Trust - a charity with the mission to preserve, protect, develop and improve local watercourses. Firstly, Chris asked about the journey water takes to actually get into our taps...

Sarah - We call that the urban water cycle, and it very much starts with taking water from the environment; as you mentioned, that might be groundwater, or that might be surface water from watercourses like rivers. And then that's treated at a water treatment plant, using chemicals and physical processes, which obviously takes energy. And then it's pumped into our houses, using more energy, and through a vast network of pipes and valves and other infrastructure. And that's the part that gets kind of expensive, both in terms of money, energy, and of course carbon emissions. And then it comes out of our taps when we turn them on.

Chris - I suppose it's not automatically intuitive that water would have a carbon footprint, but for the reasons you've outlined, it clearly does!

Sarah - That's right, yeah. So about 11% of the carbon emissions that are generated in the water production process go into the treatment and the transport; and then of course we've got heating of water in homes as well, and that can account for about 89% of the carbon that we use when we're thinking about water.

Chris - So obviously anything that translates into a more efficient use of water, and a more efficient use of hot water - that's going to translate into a carbon saving, isn't it, and that's got to be good news. In terms of what sort of share of the water that the UK uses, how big is the domestic market as a proportion?

Sarah - Approximately 49% of the public water supply goes to what we would call 'domestic use' and commercial uses, and that's household and non-household. And then about 51% goes to agriculture, industry, and energy production. So you can see that that 49% is quite a big amount.

Chris - Yes, indeed. And how efficient are we at using it? In other words, when it all ends up going down the drain, ultimately - admittedly - but when it comes into our home, how much ends up going to the intended source, and how much is wasted?

Sarah - That's a good point. In the UK we have about 20% leakage from that big infrastructure system of pipes and valves and things that I mentioned. That's actually not too bad.

Chris - Out of every five glasses of water, one has gone down the drain rather than down a person's throat?

Sarah - That's it, yeah. So that's lost in that distribution from the treatment plant to the home. So yeah, it depends on area, but if that water travels over a large area between where it's taken out of the river or the groundwater, to where it's then turned on and comes out of your tap, yeah, that that can be quite a big loss.

Chris - But in terms of the overall efficiency, then: so 20% gets wasted, but other things like the thermal uses, the carbon footprint, and so on - are their savings to be made in terms of how we use our water?

Sarah - There are, definitely. Within our home, we use about 25% in the shower, for example; 20-25% in the kitchen; but what we actually flush down the toilet is one that makes the least sense, perhaps, because we flush anywhere between 20-30% - bear in mind, this is drinking quality water - down the toilet. It depends on the type of toilet you've got, and how old it is, and those kinds of things. It's one of those questions that we have to ask ourselves: is it right that we flush drinking quality water down the loo?

Chris - It's sad, isn't it, that in some parts of the world, people are dying because they can't get anything to drink, and we're chucking the stuff down the toilet - quite literally. Is there no better way to do this? Because I often watch the water swirl down the plug hole in the bath or in the shower, and I'm thinking, "actually, I could still drink that. It might have a bit of shampoo in it, but it's a hell of a lot better than what some people are drinking for their daily water. Can't we use that better to, say, water the garden, or chuck that down the toilet, for example? Why do we throw it away?

Sarah - Indeed. It just takes a shift in thinking and behaviour, really. And what you refer to there - the water from your bath or hand basin - that's what we call grey water. And very much so, you can reuse that in the garden; or washing your car if you store it in a water butt, those kind of things; also rainwater harvesting, so that's water that falls on your roof and then it goes down your downpipe, it might go into a water butt, or it might go into a larger rainwater harvesting system. And that can be really good, because what that's doing is it's capturing water where it falls, and then you're using it where it's fallen. So it doesn't have to be transported and pumped, using energy and producing carbon emissions, to your home. And that's a really good way to bring down water use.

Chris - The thing is, Sarah, that when you look at new build houses, they still chuck the shower and the bath water down the drain. There's no policy that says, "and there has to be a water scavenging system in this design that will route that water to somewhere else useful." It's not a building regulation yet, is it? And similarly, we haven't got a system that's easy to implement in your average existing home, so a person who's minded to want to do there bit can easily do it. They've got to put a bucket in the toilet with them, in the shower with them, haven't they, to flush the toilet with, if they want to do that?

Sarah - That's right, yeah. So water reuse is recommended in lots of different building standards and different guidance, and there are some provisions in the building regulations, but they're not as strict or as tied down as they could be. I guess something to bear in mind is that the average amount of water a person uses in a day - what we call 'per capita consumption' - has dropped from about 146-148 litres in 2011-2012 to around 141 litres in 2016-2017. That varies a bit - if you've got a meter, if you haven't got a meter. But what the real aim could be - and this was under some previous green building guidance - was getting it down to around 100 or 80 litres. And that can be achieved by the things that we've been talking about, so grey water or rainwater; but also things that you can do, as simple as turning off the tap when brushing your teeth, and also putting what we call cistern displacement devices in your cisterns. That might be a thing called a hippo, which people can get from their water company, or a brick, which displaces about a kilogram of water. So there are things people can do. But also the kitchen sink tends to be the most energy and carbon consumptive, because that uses generally a lot of hot water, so there's a lot of carbon to be saved by saving water from your kitchen sink and reusing it.