Re: Thames Water
"...tables 10, 10a and 10b for meaningful stats relating to demand and deployable output, total storage volume is a meaningless metric..."
Well, up to a point. Total storage volume IS meaningless on its own - it needs to be related to average/peak input to the system and average/peak demand. If the input or demand vary considerably, then increased storage is needed to buffer the variation. If the figures do not vary much, then you can get away with little storage.
This data can be obtained from the Thames Water data and other sources, but only after a great deal of work. When you do this, you find that average input varies quite widely. Year-on-year variation of 33% rainfall either side of the nominal average is quite usual. And demand is constantly rising.
It is easy to see from this that, unless storage is increased in line with demand, we will first start to hit problems when there are exceptional years, and then this issue will increase so that problems will occur during the 'dry' parts of otherwise fairly normal years. Eventually, supply problems will become endemic, and occur at all times, even when there is quite good input. This is beginning to happen.
In 2004 the SE water companies proposed 5 new reservoirs and three extensions to existing reservoirs to cover their predictions, and avoid hitting supply problems. ALL of these plans have been rejected at the planning stage by government inspectors, who appear to be applying a 'demand management' strategy rather than a 'supply management' one. There has been no discussion of any need or justification for this, and it appears to be based on a mistaken concept of water as a 'scarce resource'. It is not, of course. It is an infinite resource which passes through us in a cycle. We can store as much as we want to, and our storage will not affect the sum total of water available to the world one bit.
The typical argument you will see in the rejection of these plans is that:
"...this reservoir will not be needed if demand can be cut by 20% in accordance with government policy..."
This is true. If we cut our demand by 20% (which is the figure specified in the government's water strategy document "Water Futures"(2008), then we will not have this problem again until the SE population rises by another 20%. What is rarely mentioned is that the cost of 'cutting demand' (beyond a few small token projects) is high. Providing rainfall storage on all commercial buildings, for instance, is nearly 100 times more expensive than providing a reservoir and supplying the same amount of water to the buildings via the mains.
The other thing that is not mentioned is WHY we should be doing this. 'Saving water' does not actually 'save water', because water is never destroyed. What it does is 'save centralised infrastructure expenditure'. At the cost of greatly increased local infrastructure expenditure. And, if you are worried about environmental issues, using localised infrastructure is vastly less efficient, uses much more energy, generates much more CO2, and is much worse for the planet in every sense.
So why do we do it? I have not got any answer for that. It makes no sense from the figures. I believe that it is happening because the magic words 'save' and 'environment' can be wielded by a 'green' policy maker, and because NOBODY in a policy position is able, or wants to, understand a mathematical argument....