Short answer: in most urban settings, yes—a domed top will usually keep rain out better than a flat lid. But the dome isn't a magic shield. It works for a simple reason: water runs downhill. A curved or sloped top sheds rain to the sides instead of letting it sit on top or seep through seams. A flat lid can do fine if it's tightly fitted and slightly sloped toward a drain, but many flat lids end up with standing water, especially if they warp, dent, or collect leaves. That standing water finds weak spots: hinges, gaps, vent holes, and the opening itself.
The biggest advantage of a domed top is how it protects the opening. Many urban cans have side openings under a curved hood. The hood acts like a little roof, so rain falling straight down or at a mild angle hits the dome and rolls off before it reaches the trash. That keeps the contents drier, reduces smell, and cuts down on leachate—the nasty liquid that forms when rainwater mixes with garbage. In busy city areas, that matters because wet trash is heavier, messier, and more expensive to collect.
That said, domed tops are not perfect. Wind-driven rain can blow sideways right into the opening. A dome with a wide mouth, shallow overhang, or poorly placed vents can still let water in. Some domed cans also have a recessed top or a gap around the dome, and if the drainage path clogs with leaves or litter, water can pool in the wrong place. A flat lid with a good gasket, a tight seal, and a slight slope can actually outperform a badly designed dome.
So the real answer is: domed tops generally win in rain, but design details matter more than the label. If you're comparing two cans, look at the opening orientation, the depth of the hood, how the lid overlaps the body, whether there are drainage holes, and how the lid seals. For an open or loosely covered urban trash can, a dome is a clear improvement. For a closed, well-sealed can, a flat lid can be just as rain-resistant—sometimes even easier to clean and empty.
In short, yes: domed urban trash cans usually keep rain out better than flat lids, especially when the opening is sheltered. But they're not waterproof. They're rain-shedding, and how well they do that depends on the whole design, not just the shape of the top.