It's a made-up media story. In the old days cold water came from the mains and hot water came from a storage tank in the loft where it could be contaminated and

It's a made-up media story. In the old days cold water came from the mains and hot water came from a storage tank in the loft where it could be contaminated and for that reason hot water was considered unsafe for drinking. Another reason was difference in pressure which could force water coming from one source into another.