Fishmonger, not meaning to be argumentative here, but did you also eat food prepared by others in those several weeks before your symptoms? Maybe swim in a public area?
Your case sounds quite similar to the "smoking gun" case back in the 1970s -- hikers got giardia, so it was obviously the water. It has since been shown that the incubation time, and the lack of any evidence of giardia in the water in the area where they camped, point to some other source of their giardia infection. But that erroneous study started the huge rush to water filter use.
Several years ago, I had giardia. Doctor confirmed it. County health people called me. I said I had been out hiking and drinking untreated water. The person didn't even care that my hike started just four days before the first symptoms. Scientific studies show it takes 7-10 days. So I got it from someplace around home. Daycare situation, swimming pool, some fast-food -- who knows?
But based on the timing, it wasn't the water.
