Faulty plumbing may well be a contributing factor in river pollution but worse than this is the cleaning of vans and cars in streets and forecourts (Faulty plumbing causes flow of stream pollution', February 1).

All this filthy water, which contains oil, grease and dirt, is permitted to flow into surface water drains when it should go into the sewers. How this could be stopped is another question.

At least those who use the facilities at service stations are not guilty.

In the summertime when streams are at the lowest rate of flow, effluent from car washing can represent a considerable proportion of the total of streams that run through built-up areas.

Bernard H Oak

Quakers Lane, Potters Bar