I was exposed to water on Ft. Hood Texas after a week of very heavy rain. We had to drink that water in the field since we were on foot and without any large unit support. There were cattle in the area, lots of cattle waste and the only method to purify water was issued iodine tablets.

Within a few days of returning home I began an alternating bout with diarrhea and vomiting. This lasted about a week before finally letting up slowly. After that trip I bought a water filter. I also learned more about the iodine tablets and found that if they are green they have lost their strength and needed to be replaced. I also lost the tablets in the field, having them stored in the little pocket on the canteen cover (USGI) is almost a guarantee that they will end up falling out somewhere.
I was never sure of the exact ailment, other than it was ugly and I have avoided it since.

For sure, keeping hands and kitchenware clean are important, both at home, on the road and on the trail. I even use hand sanitizer after pumping gas to keep from getting something off that pump handle.