Opinion Last month in old London town and across England, formal water rationing came into force again for the second time in just six years - and the creeping rationing of water meters continued to spread. Despite the rainiest April since records began, government minsters are openly speculating that total mains cutoffs and standpipes in the street may be required next year.

And yet, astonishingly, it would require only a small investment - far less than has been spent on fixing leaky pipes in recent years - to render the capital's water supplies completely and utterly drought-proof, forever. All the fresh, drinkable water the city's population requires for its taps, its showers and its hosepipes could be produced without taking a drop from rivers, aquifers or reservoirs, at minimal cost and with only a tiny impact on energy use and carbon emissions.

In short, Britons' water is being needlessly rationed in a staggeringly pointless effort to limit energy consumption and carbon emissions by a very small amount - a move driven, as is so very normal, by a political (and civil service) agenda which seems completely divorced from the hard numbers surrounding the issue.

Londoners vote tomorrow in the capital's mayoral elections, but both candidates, it seems, would rather prepare people for more stringent rationing (to the point of poor hygiene and serious health risks) than make any attempt to sort matters out once and for all.

Here are the hard numbers in a nutshell, using London as a case study for the whole of the UK - and indeed the entire developed world.

Average normal water consumption by the capital's 8 million people is 167 litres per person per day: just to be clear, this includes the use of hosepipes for watering gardens, washing vehicles etc. Almost all of this water at the moment is taken from rivers or extracted from groundwater. These supplies are finite and depend ultimately on rainfall. As the city's population has grown, it has gradually become the case that they may not cope with demand during prolonged dry spells.

But modern technology can be used to cheaply turn seawater, the supply of which is effectively infinite, into fresh drinking water by desalinating it. Alone among British water companies London's Thames Water does actually possess a single desalination plant, at Beckton on the Thames Estuary, but this only has the capacity to produce 150 million litres a day - less than 10 per cent of the city's requirements - and it is run at low output or completely shut down most of the time.

In general, desalinating seawater in a modern reverse-osmosis plant like Beckton requires the use of 7 kilowatt-hours (kWh or "units" on your electricity bill) of electrical energy to produce a tonne (1,000 litres) of drinking water. In fact, Beckton requires significantly less energy than this as estuarine water is not as salty as seawater proper, but this article is meant for a wider audience than just Londoners, so let's assume 7 kWh/tonne to begin with.

In order to make all the water a person requires, then, a desalination plant needs approximately 1 kWh per day. A kilowatt-hour, purchased on the wholesale electricity markets, can generally be obtained for six pence or less at the moment: the necessary energy would cost a water company say £22 per person annually.

Total electricity cost for a whole year's water supply from the sea, London wide? About £176m, less than Thames Water's profit margin even in hard times; much less when the company is doing well. And of course in reality there would be no need to use desalination for the entire supply (this would actually cause flooding 1 ). Also, in reality, we are speaking of brackish water not brine. So we can see that using desalination to make London drought-proof would cost very little.

But what about capital investment? Maybe desalination plants are really expensive. Maybe that's why we only have one proper one in the whole of the UK, and why we are so often told there's a drought on and we must expect hardships.

Nope: Beckton cost just £270m to build. Another 15 such plants - enough to provide London's entire water supply if required - would cost approximately £4bn, an investment of just £500 for each person living in the city. Enough desalination plants to provide half the supply, which would make the city completely drought-proof for the foreseeable future, could have been built for less money than Thames Water has spent reducing leaks in the last nine years - and the leaks programme, while highly disruptive to the city as roads have been torn up in order to replace old pipes, has delivered only comparatively minor water savings.

So that's the reality of water supply and modern technology. For a trivial cost, we can make all the fresh water we need out of seawater.

So it's really very plain that there's no possible excuse for ever imposing standpipes or hosepipe bans or any other form of water rationing on Londoners or indeed anyone else - certainly anybody who lives in a developed nation within reach of the sea (the great majority of the human race lives near the sea or tidal estuaries connected to it). Modern reverse-osmosis technology means that we can use small amounts of energy to make as much fresh drinking water as we want, and the costs are small enough that the resulting water is too cheap to meter. Running an oven for an hour or two, remember, consumes enough energy to make an entire tonne of water.

And yet here we are in the year 2012, in one of the planet's greatest and richest cities, with water rationing in force and worse rationing being foretold. What on Earth is going on?

Briefly, politics is going on. The former London mayor, Ken Livingstone, virulently opposed the building of the Beckton desalination plant. His successor, the extrovert bicycling media-tart Boris Johnson, allowed Beckton to go ahead. Yet it is still official London government policy under his administration that "desalination is considered an emergency measure and is not a long-term solution for future supply needs".

This picture is echoed nationally, with the head of water at the Environment Agency telling the BBC that "you don't want to rely on desalination".

Why?

If you ever actually drive your car, washing it with desalinated seawater isn't worth worrying about

Because, we are told, desalination is "carbon intensive". That is, the energy used in a reverse-osmosis plant involves serious CO 2 emissions.

Is that right? On the face of it we're talking about a lot of energy here, no less than 2,920 gigawatt-hours per year in the every-drop-from-seawater case for the whole of London's supplies. That equates to a hefty-sounding 1.25 million tonnes of CO 2 emissions each year.

Maybe we should, in fact, stop watering our gardens, stop washing our cars - even stop washing our clothes and ourselves, as some scientists advocate.

But in fact this is a foolish argument to make. That one kilowatt-hour per day for each of us to make 167 litres of water from sea brine is actually trivial. Each Londoner already uses 52 kWh every day on all his or her other, hugely more significant, energy expenditures - transport, heating, cooling, lighting and the rest. Normal non-London Brits, who live in different kinds of buildings, who drive more and use public transport less, get through an even heftier 70 kWh or more daily.

The fact is - and this applies everywhere, not just the capital - if you ever drive your car, washing it using a hosepipe fed from a desalination plant adds almost nothing to the energy you use. If you heat water up at all (that is if you use it for cooking or washing, which accounts for the vast majority of domestic water use) the fact that it is desalinated seawater means almost nothing in energy terms. And if you use a hosepipe to water green growing plants in urban terrain, the fact that you are helping take carbon from the air and reduce the urban "heat island" effect in hot summers certainly outweighs the small amount of energy required to make that hose water from pure brine.

In the reality right now, where most London water would still necessarily come from rivers and boreholes in order to prevent floods and we'd be desalinating not sea brine but merely-brackish Thames estuary water, the effect on energy use and carbon emissions would be completely imperceptible: an increase of a very small fraction of a single percentage point.

Even the most hardline extremist greens, who take it as a solid fact that carbon emissions are a deadly threat and must be reduced at any cost, would - if they were thinking sensibly - surely hesitate to expend any serious amount of their sharply limited supply of political capital, of hard-won public goodwill, on achieving such a tiny carbon reduction. This is all the more so as hosepipe bans during rainless summers actually make cities less green. A green campaigner wanting to reduce energy use and carbon emissions would achieve more by doing almost anything else: persuading people to use public transport, insulating buildings better, battling against patio heaters, encouraging less washing etc etc.

But the Greens don't have to expend any political capital on this, as mainstream politicians have decided that desalination is bad already. There can't be anything much crazier than presenting desalination as a significant environmental problem and using political power to suppress it - and then using political power again to ration people's water to deal with the artificial "drought" that political idiocy has caused. But that's what London - and national - politicians are doing.

But come on - surely it can't be the Greens and the mainstream politicians' fault, not when there's a multibillion-pound monopoly supplier like Thames Water in the picture. Certainly the company's customers, watching their bills surge upward as their gardens, parks and cars turn brown and dusty this summer, will not be pleased to hear that Beckton is shut down right now and that it ran at a measly 10 to 40 per cent of full output in March 2 ; though a company spokesman assures The Register that it will be "running throughout the summer" and that there "may be days" where it is run at full power, depending on demand and rainfall in the months ahead.

That's not very impressive, though, when Thames Water has had the cheek to impose a ban on hosepipes using delegated governmental powers which it can employ at its own discretion. Running Beckton at full power wouldn't cost Thames Water much, as we've seen - but simply ordering a hosepipe ban costs the company nothing at all.

But to be honest, given the imbecilic political climate it was operating in, Thames Water probably deserves quite a lot of credit for getting Beckton built at all. Left to itself there can't be much doubt that the company would have built more Becktons as this would have achieved a lot more at less cost than digging up pipes and replacing them - though of course Thames Water is reluctant to say so for fear of drawing more flak from numerically illiterate Greens and journalists.

Instead the company has felt compelled to spend billions on reducing leakage in its pipe network by a relatively paltry amount 3 - money which could have built more desalination plants and made London's water supplies drought-proof by now. There's no doubt that a lot of the city's aged Victorian pipes needed (and that many still need) replacing, but this was plainly not the most cost-effective way to spend the money with a serious supply shortage going on.

City Hall says 'talk to the Mayor' - Mayor says 'this is one for City Hall'

So there is no shortage of water worldwide and there is no drought in England or in London. Supplies of water on this planet are not actually without end - even the oceans aren't truly limitless - but they are infinite in a practical sense. There is no possible excuse for rationing the domestic water supply of anyone who lives in a developed economy with access to a water-grid connection. The fantasy problems of "virtual water" and "water imports" aren't within the scope of this article (though they are also the product of Green extremists and a total failure to grasp numbers 4 ).

The problem of water rationing is political, not environmental or technical. Politics varies around the world, of course. But this article uses London as a test case, so it makes sense to examine London politics to finish up - all the more so as London assembly and mayoral elections are imminent.

Of the two main candidates, Labour's Ken Livingstone has made himself perfectly clear by opposing even the limited capabilities of Beckton. He stands for needless water rationing.

But what's the position of incumbent Mayor Boris Johnson, the only other person at all likely to win the election? He gave Beckton the nod, though only on the basis of it being an "emergency measure".

We got in touch with Boris' campaign a fortnight ago, suggesting that the Mayor might like to say something along the lines of "vote for me and I'll put an end to drought FOREVER". A deafening silence ensued.

Having chased up Boris' team several times, we finally got a quote today. A spokesman said: "This is a matter for City Hall," meaning that it was something that the permanent civil service should decide, not politicians.

We had actually anticipated something like this, and funnily enough we had already asked City Hall why rationing was considered acceptable when Beckton was shut down - and why on Earth we weren't building more Becktons instead of digging up pipes and preparing the public for more rationing next year.

City Hall were similarly reluctant to answer, but they eventually told us:

There are a number of queries here that are really for Thames Water to address. In terms of the mayor's views, because we are bound currently by pre-election guidelines, I cannot provide more ...

We were also referred to The Mayor's Water Strategy, which again describes desalination as "an emergency measure".

To sum up, then: nobody is offering you a choice on this. There is complete consensus among the governing classes, elected and unelected alike, that Londoners (and Britons more generally) will soon face stringent water rationing in order to save a small fraction of a single percentage point on carbon emissions. In other words for no good reason at all, even if you believe carbon emissions urgently need to be reduced.

It's hard to avoid the conclusion that scientific and technical illiteracy is becoming so rampant as to make democracy an unworkable form of government. ®

Bootnotes

1 Groundwater extraction in London by heavy industry had lowered the city's water table to no less than 88m below sea level over a long period up to the 1960s. As industry has departed, this has risen to 35-40m, enough to cause concern that Tube tunnels and other vital underground infrastructure might start to flood. In west London, where not much groundwater is extracted for public supplies, the level is still rising - though the problem is no longer thought to be urgent.

If no water was taken from the Thames and the Lee - more than half of the city's supplies are taken from high up in these two rivers, later to be discharged much further down the waterways in various forms - it's a certainty that they would burst their banks and cause surface flooding much more often.

Most of the figures in this article come from the Environment Agency's State of the Environment for London 2011 report.

2 It should be noted that water produced from Beckton (or anywhere else) can be stored for use later, by putting it into reservoirs or the North London Aquifer Recharge Scheme (NLARS), a system of boreholes which use subterranean aquifers in effect as underground reservoirs. Beckton could have been running at full pelt since it was commissioned in 2010: if NLARS and the reservoirs aren't full to the brim right now, Thames Water has only itself to blame.

3 Leakage today is down to 600 million litres a day, meaning that London actually needs supplies increased by half again over what people use. Nonetheless, it has cost billions to cut that figure from 900 Ml/day: in other words to achieve savings of 300 Ml/day. Two Becktons, able to supply that same 300 Ml/day, would have cost only £500m to build and perhaps £20-30m annually for electricity - leaving billions more to spend, which could have built many extra desalination plants to make the city truly drought-proof by now.

4 We are told that "I had a cup of coffee on the way to work: 140 litres of water were needed for that single cup". Assuming this to be true, then, power requirements to desalinate that much seawater would have been a tad under one kWh - enough to increase the cup's price by a few pence and with similarly inconsequential consequences to its energy and carbon footprints. "A single pair of jeans, for example, requires about 11,000 litres." (Desalinate all that water, add a few pounds to the price at most). Etc.