Bought a house in Arizona in July, and it's been fine... Until a week ago when I started to notice an odor in the shower. It took a few days to locate the source, but then I discovered that it's the drain. It smells like cat pee or ammonia. Then I noticed it in the other bathroom shower. And a day later, in the kitchen sink. It's getting strong, and seems to get stronger when water is run. It's so strong that just walking by the bathroom is smelly. Anyone have any idea what is going on?? We have really hard water, but we haven't made any changes to the house, plumbing, pipes, etc. This is getting gross. I'm hoping someone has experienced and resolved this before. The kitchen doesn't share a wall or anything with the bathrooms.

there should be traps under the showers and the kitchen sink to keep sewer smells out of the house. it would be very unusual for three of them to lose the water in them without your hearing a gurgling sound.
might as well get a couple of bleach and dump it down the drains. (good place to start)..

Packy has given you good advice but do you have a cat? This is probably stagnate water. Be sure you fill all the traps, even the one in the wall for your washing machine if you have one. Flush out with plain water after you put the bleach in and let it set for a couple of hours. If you still have a smell problem, call a qualified plumber.