Drinking a cup of coffee or walking the dog would be just as perilous. You can compute the danger of dying in a road accident over a period of 70 years at far less than one in a hundred, but the risks here are too infinitesimal to be worth computing. Living is a risky business which ends in death. Mankind is prey to sudden awful viruses, and vigilance is always necessary. Smoking does damage your health.
Pesticides can poison the water.
But living is also a matter for reasonable inquiry, reasonable doubt and reasonable conclusions. When we call in the experts, we should expect no more than the best tools for risk assessment. Sir William Stewart gives us those tools. It would have been better if he'd stopped there, in brevity and prudent clarity. When there is nothing sensible to be done, it's best not to do it.