Mixed taps are all over the US and many other places in the world and have been for a while and we have no water safety issues from this. Water safety has nothing to do with it:
"Most bathroom sinks in Britain still have separate hot and cold taps today, 60 years after Mr. Churchill’s conversion and decades after nearly all dual taps were scrapped in the U.S. and most vanished from continental Europe. For reasons of thrift, regulations and a stubborn attachment to tradition, the British have resisted the tide of plumbing history. Even when they renovate old homes, many choose two-tap systems, and builders often install them in new, low-end housing. Separate taps account for an estimated 40% of all bathroom-faucet sales in the U.K."
"Most bathroom sinks in Britain still have separate hot and cold taps today, 60 years after Mr. Churchill’s conversion and decades after nearly all dual taps were scrapped in the U.S. and most vanished from continental Europe. For reasons of thrift, regulations and a stubborn attachment to tradition, the British have resisted the tide of plumbing history. Even when they renovate old homes, many choose two-tap systems, and builders often install them in new, low-end housing. Separate taps account for an estimated 40% of all bathroom-faucet sales in the U.K."
From: http://blogs.warwick.ac.uk/mhillebrandt/entry/british_peculi...