What would happen if it rained in Lima?

The streets in Lima are kerbed and guttered, but there are NO drains. Houses have driveways that slope down to the house with no drains. 

No need to worry it does not rain in Lima.

Many of houses do not have roofs - I have heard 2 reasons, it does not rain therefore no need for a roof, perhaps the real reason is that until you put a roof on your house it is not completed and therefore is not taxed.