Dave - It's looking like it would be a very dry, hot year this year in the UK with some reservoirs currently about 20% lower than normal. So good water management practices are essential. David Butler is from Exeter University where he's professor of water engineering. Hello, David. How much water do we actually use in a day?

David - We all use individually about 150 litres, so just imagine a litre bottle of water that you might have in your fridge. That's a 150 of those we all use.

Dave - So, how much of that is actually vital that we can't reduce as it were?

David - Of that 150, the amount that we actually drink or cook with is far, far less. Perhaps just something like 1/10th of that. 10 or 15 litres.

Dave - So we've got this huge amount of water we're using and I guess agriculture must be putting a lot more on top of that. So, what are our options if it's kind of getting dryer and we're getting higher population? What are our options to improve our use of water?

David - You know, we're being squeezed on all sides really as you say with climate changing and with a growing population. So, we need to try and attack the problem in a number of different ways right from the small scale up to the large scale. So I think it starts really, individually in the house. We need to be perhaps more efficient in the way that we use our water in our everyday life. Because of course, we can recycle water in the household as well. We can take our gray water from sinks and showers, and re-use that for flushing toilets for example. So that would potentially reduce our water consumption by up to a third.

Dave - So what do that actually involve? Does that involve changing the plumbing of a house?

David - Yes, it would do a little bit. You would need a system that drained your shower and your sink and collected it into a tank somewhere in the household and then some form of treatment and a pump to get it back to your toilet.

Dave - But you're still left with that 2/3 of our water usage. So what can you do with that?

David - Another angle to this is to think about how water is actually delivered to the household. Although we use this 150 litres, the pipe system that brings the water to the household also does leak to a certain extent and typically now, leakage levels are something like 20%. So 20% of all the water that's delivered is lost along the way.

Dave - That's really scary. Is that sort of just because there's a very, very old infrastructure in the UK?

David - Yeah, that's right and the water companies have been working hard at reducing those levels. Not so long ago, they were up at 30% plus, so they've been pushed down now by careful management and by renewing some of the very old pipe work that we have in the UK.

Dave - Okay, so we're trying to save water that are coming into the house and when it's in the house. But at some point, we're going to want to get rid of all of these waste water. What do we do with it then?

David - Well, with waste water itself, that can be another resource of water. At the moment, it's very common for our waste water to be treated at a series of treatment works and then that will be discharged into a local river. It's then not uncommon downstream for the next town to take that water out, treat it to drinking standards and to use it. So actually, it's one integrated water cycle.

Dave - So essentially, you can keep recycling the water. Is there a limit to how often you can recycle water?

David - I don't think there's a limit as such. Look at the river Thames and think of all the towns up and down the river Thames and with London at the mouth of the river, the water itself has been used and re-used many times. I think the difficulty can arise if you do that in too tight a loop. That's a very loose open loop, you're taking water in and out of the environment, But once you tighten that loop very closely, then I think there could be some danger of pollutant build up.

Dave - So we've got various different approaches. But I guess the first thing, if you're a politician, you want to know what's the best bang for your buck - where should we be first spending our money in this way?

David - Well I think where we should probably try and spend our money is first of all, to make sure that we use less water. One way of doing that is for metering of properties. Across the UK now, something like 30% of households only are metered and studies have shown that households with meters tend to use less water, maybe 10% or so less water. So, merely the act of putting a meter in seems to reduce water consumption. So that's probably as good a place to start as possible. Otherwise, you're into very large scale engineering works such as constructing new reservoirs.

Dave - I guess in other countries, that leads on to the other half of water management and that's floods. I mean, it doesn't seem very long ago, just into kind of wading around in lots of water. Is there any way of storing that, reducing the flooding problem and storing more water for when we really need it?

David - Yeah. It's a bit of a holy grail that is and you're right. One minute since we have a drought and the next minute we seem to have a flood. And I think that's something to do with climate change that we're seeing this variability and we're seeing more extremes being predicted and we're seeing more extremes. What can we do about it? Well probably, storage is the answer and rainwater harvesting is one possible way to do that. You can collect rainwater from your household roof. Now if you put a big enough tank in there, that means you can use some of that water for toilet flushing for example and therefore save water and if the tank is big enough, the space there to collect rainwater, to stop it running off and causing flooding.