I found one ant in my bathroom...are more on the way?

I found an ant in my bathroom this morning, on the floor. I keep a tidy bathroom and there are no spillages etc. Is there a chance this could be a one off or do they always colonise and can I expect more? If so, are there any short-term solutions? I'm on my year abroad in madrid and I only have 2 months left until I go home so I don't want to shell out on pest control for two months. Thanks