.... and Wee Weasily should maybe also have pointed out that whilst we ( Pilots ) have to eat different meals from one another, there's no such requirement in place about the drinking of water from different sources.
E.g. we all drink the tea & coffee made from the water, which comes from the aircrafts potable supply and where this said same water is not always heated to boiling point ( or beyond - which would kill a lot of bacteria ) but it is used to make our drinks...... i.e. it's often heated to just above teppid, has a tea bag dunked in it for 30", and then is passed to the pilots for them top drink - so go figure !
That said Andy, I too take your point that the ingestion of a little bit of good honest dirt never did much harm - it's the really fithly dirt which does that !
