Your ethical dilemmas sorted

I know cars are evil and all that, but what's the best way to wash one?

K Fallows, London

You only need to look at a car wash's soapy, flailing brushes to realise how profligate they are with water, right? The industry, you might not be surprised to learn, believes this assumption to be an unjustified slur on its good name. The International Carwash Association, based in Chicago, claims that washing your car yourself can use "up to 10 times more water" than taking it to the local car wash. A professional wash, it says, uses an average of 121 litres of water. Logic suggests, though, that you would really have to be extremely free and easy with your garden hose to use more than 1,000 litres of water - equivalent to more than seven full-to-the-brim baths - to wash a car yourself. By using just a bucket and sponge, you can easily keep it down to just a dozen or so litres.

Somewhat perversely, professional car washes were exempt from recent hosepipe bans, but some are now making more determined steps to lower their water consumption. For example, last month a company called Pit Stop in Swansea was a winner at the Environment Agency Water Efficiency Awards. The firm uses a reed-bed and settling-tank water recycling system that has reduced its water use by 60%. So it is worth asking a car wash exactly what system it is using. The frequency with which you clean your car is also clearly key. It's just one reason to be thankful that the suburban ritual of cleaning the car every weekend seems to have receded into history. The "clean me" finger-writing test seems to be much more appropriate.

But even if you manage to be miserly with the water there is still the issue of run off to consider. If, as most people do, you wash your car in the street or on the drive, the suds will typically enter the stormwater drains, and not the sewers. This means that the dirty water is likely to enter a nearby river untreated. For this reason, many local authorities now recommend that you park your car on a lawn or gravelled surface before washing it so that the dirty water drains into the soil instead. Alternatively, there are a number of "waterless" car wash products on the market making various eco claims, but the majority rely, just like your car, on petroleum-based ingredients to work.