Britons pay for electricity and gas by unit - why not water? Perhaps then we might notice how much gets needlessly flushed down the drain.

It seems as if it rains all the time in the UK, yet the taps could run dry within a few decades. Water stores throughout Britain are stretched to the limit, yet we continue to use the stuff as if it's going out of fashion.

"It may be gold, but does it have a dual flush?"

Each Briton uses about 150 litres a day for washing, cooking and flushing, says Ray Kemp, an Environment Agency spokesman. "If we each had to fetch and carry that amount of water, we'd have to fill 16 buckets or buy 75 two-litre bottles every day."

Even before it gets to our taps, one-fifth of the water supply is lost through leaky pipes - an improvement on a decade ago, when water companies let more than one-third seep away.

Annual rainfall in...

Essex: 525 mm London: 593 mm Rome: 744 mm Barcelona: 587 mm Jeruselem: 529 mm

Yet less rain is falling from the skies to top up the reservoirs. When it comes, it is heavier, but the annual rainfall from the grey skies of south-east England - where the bulk of the population lives - is actually less than that in sunny Rome.

No wonder supplies are under pressure.

One way for households to save both water and money is to install a water meter. Currently just one in four houses is fitted with such a device.

The National Consumer Council, which this week publishes a discussion document on water charging, believes there could be a case for metering in areas with shortages (and discounts for those least able to pay).

The UK is getting heavier rain but less often

But "user pays" is not sufficient to encourage people to save water, says the council's Maxine Holdsworth.

"The maximum that people with water meters save is 8% of their water usage; and deciding to use less water is much like trying to convince yourself to go to the gym - sometimes you do it, sometimes you don't."

Also, individual efforts can only achieve so much. It would be far more effective for the government, suppliers and the building industry to support sustainable, community-wide measures.

How much water washes away?

Toilet flush: up to nine litres Brush teeth with tap running: six litres Garden sprinkler: 1,100 litres an hour

As it is World Toilet Day, it seems appropriate to start with the humble loo. The UK could follow New York's lead and provide rebates for householders to replace old-style toilets with dual-flush models, which have a "half-flush" setting to carry away liquid waste.

"This meant a huge outlay for the New York authorities, but it meant that they didn't have the extra expense involved in building a new reservoir," Ms Holdsworth says.

Rather than use fresh water to flush toilets, a cistern fed by rain water or grey water - the run-off from showers and sinks - could be used.

Unless such measures become the norm, we could face a future where water no longer comes on tap.

Ways to save water

Take a brisk shower, not a leisurely bath. "If you took a shower rather than a bath each day for a week, you'd save enough water to make 1,680 cups of tea," Mr Kemp says.

Choose appliances such as dual-flush toilets, and washing machines and dish washers which use less water.

Only flush toilets if really needed; an Australian maxim goes: "If it's yellow, let it mellow; if it's brown, flush it down."

Or put a "hippo" in the cistern - a polythene box which stores one-third of the water instead of it being flushed down the drain.

Wash fruit and vegetables in a bowl of water rather than under a running tap, then use the water on your plants.

Wash clothes with your flatmate's instead of wasting water on half-empty loads. The average family uses 26,000 litres of water a year just on laundry.

Nappy washing services use 41% less water and one-third less energy than home washing.

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