Science Questions

Does salt, put on the roads to prevent iciness, get into the water table?

They say they’ve just put 20,000 tonnes of salt down on the roads, most of which goes into the ditches which go down to the water table. I’m just wondering how long is it going to be before in a drought we’re not going to be able to drink water in the ground because it’s brackish. Greck, Essex

Dave - That’s a good question. Yes, all the salt is going to go down to the water table eventually, it’s going to dissolve in water and run down where water is. It’s either going to run down the streams and down into rivers and out into the ocean where it’s not going to make much difference. The stuff which goes into the water table will make some difference. Locally it could be an issue. We are expecting when you put the salt down it will have a significant effect on the degree of saltiness in the ditches down the side of the road. Overall it’s not going to be very big an effect just because of how big the UK is. 1mm of rain over a square kilometre is the equivalent of a thousand tonnes of water falling on the UK. The UK’s 40,000 square kilometres so just one millimetre of rain, less than a 20th of an inch is going to be equivalent to 40 million tonnes of water.

Chris - Although to be honest that’s not all falling evenly and uniformly like that. There could be some areas that could end up with local salt build-up but it’s trivial in the grand scheme of things.

Dave - If it’s in a big enough area there’s going to be enough rain to dilute it down where it’s not going to be a problem to drink.

February 2009