Hi-
I know what you're going through, I see it often here too. May I suggest my opinion here.
I think you can link this problem to one of 2 things, most likely.
The first one is a FUS. Which is basically a urinary infection in a cat. It's pretty common in cats and needs medical attention. If you can't get to a vet right now, I can tell you how to treat it like it was FUS without having to go in. I know not everyone, my self included, always has a few hundred dollars laying around to spend on vet expensise at the drop of a hat. So it could be an infection.
The second would be behavoral. Some cats, when they are mad or stressed (like a cat who has too many other cats in the house, and they feel crowded, or a cat with kids who are tormenting it) will go and pee to get it's owners attention. I have a boy here, I'm still decideding what to do with. He pees on stuff because he doesn't like the other 3 cats in the house. He's stressed, even thought the other cats are very nice and never harm him. He just likes to keep to himself and stays in pretty much one room. I know this is his problem, as he was previously in a one cat household and never had a problem there. I took him to the vet 3 times to be tested for a urinary infection, and it was nothing. This tells me that it's the other cats.
Good luck! If I can help in any other way, email me and I'll do what I can :)