Local water cycles are also influenced by the way we plan our cities: When land is paved, water cannot soak into the soil. It runs off these hard surfaces very rapidly, so pipes are needed to rapidly carry the resulting large volumes of stormwater to the nearest stream or beach. The result is that streams carry less water or dry up when it is not raining and flood when it does. Pollutants on roads and yards are also swept into waterways (see also sustainable sanitation).