new intown - Washing your car outside your house carries a heavy fine (QR10,000 or QR15,000 have been quoted). It's not 100% clear whether this law exists to stop water being wasted, or to stop dirty water settling in the streets and turning into mud.

Either way, water is a precious commodity in Qatar and shouldn't be wasted. I think the water used at car wash shops is industrial water (i.e. it hasn't been treated to make it suitable for drinking).