Why is my water making me sick?

I just moved into a new apartment. Drinking the water from the faucet – whether cold or after being boiled, for tea – makes me feel sick to my stomach for about half an hour. I seem to be fine when using it to cook pasta or rice, though.

Anyway, my county’s water is supposed to be really clean, and the water in my old apartment a couple of blocks away was fine, so I’m thinking it’s some kind of buildup in the pipes or something of this apartment. It’s really old, circa 1930s, and not well taken care of.

My question is, what kind of mineral do you think this is? Is there any way to tell? I don’t think it’s iron because the water doesn’t look rusty. Is there some sort of test I could do that is free/cheap? I’m getting a brita pitcher asap, but I want to satisfy my own curiosity and assure myself that it really is the water.

Thanks!