Why is Nebraska tap water making me throw up?

I'm from the eastern Maryland near the ocean, and I just went on vacation with my husband to visit his family in a small rural town near Grand Island, NE. Most of their water comes from a reservoir. The morning after I got here, I got really sick from drinking a cup of tea brewed from their tap water. It was so bad, I thought I had salmonella or something at first, so I kept trying to drink the water to rehydrate, and even a little sip would make my stomach hurt something awful, and I would throw it all up within 5 to 10 minutes. I couldn't hold any liquids down for 12 hours or so until I thought to drink some Coke. The Coke went and stayed down fine, and within about 15 minutes, I was all better except for a slight headache from dehydration. This morning I felt nauseous even just taking a shower in the water (which is weird since I didn't have that problem yesterday). I know my husband's family mentioned they have really hard water, but I can't see how it would cause me to get that sick! I drink from the tap in Maryland & DC all the time. Why is this happening? Is it possible I'm allergic to the water? I'm stuck here for a week. What do I do?? (PS. This is not a troll!)