So why is it?
Well, it's a matter of sewage. San Francisco just doesn't have enough of it. And what we do have is single-pipelines, which obviously can't hold as much rainfall as double-pipelines, the kind of pipelines most cities have. In fact, the American Society of Civil Engineers issued a report last year on the State of Our Sewers and determined that if we were to be graded, we would get a D+ and avoid getting an F only because because we bought them an apple and stayed after class a few days to clean the erasers. It doesn't help that our sewers are falling apart too.
So what can be done? Well, the water department came up with Sandbag Saturdays (wheee!) to help people put up sandbags when it rains. Then there's trying to fix our sewage problems and as well as demanding that new buildings being add more sewage space.
We shall see. But until then, we're going to keep on being puddle jumpers.