Living in a rainy climate definitely brings concerns about outdoor items, and your question about trash cans filling with water is very valid. The good news is that most modern urban trash cans are specifically designed to handle wet weather.
While not entirely waterproof, quality outdoor bins feature strategic drainage holes at the bottom. These allow any rainwater that seeps in to escape, preventing the bin from becoming a stagnant water reservoir. The lids are also crucial; they are designed to create a tight seal that minimizes the amount of rain that can enter in the first place, even during sideways rain.
However, for this system to work, proper use is key. Avoid overfilling the bin, as this can prevent the lid from closing completely. Also, be mindful of what you throw away. Lightweight, absorbent materials like paper or cardboard can become a soggy, heavy mass if they get wet, potentially blocking the drainage holes. Using a bin liner bag is an excellent extra layer of protection, containing the waste and making it easier to remove without leaving a mess inside the can.
So, while a torrential downpour might get some water inside, a well-designed and properly used urban trash can will effectively drain it away, keeping the mess to a minimum.