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Maybe if you'd had one of your kids spend weeks in intensive care with kidney and liver failure as a result of swimming in a lake and ingesting just a little water, it would be easier.

I think you misunderstood me, dd.  I do understand someone who advises against using un-filtered water for washing AND against swimming; both out of fear of getting sick. 

What I do not understand is one who advises using un-filtered water for washing BUT is unconcerned about swimming.  It seems to me the latter would pose a greater risk.  (Given the millions of people who have for years swum in lakes throughout Canada and US wihout a public health concern about Giardia being raised, I have evaluated the risk from swimming as negligible but can understand how others may be more cautious.)