Most of the water falling as precipitation returns to the atmosphere by evaporation and transpiration. When precipitation falls on land, it collects in rivers and lakes, soil, and porous layers of rock, and much of it flows back into the oceans, where it will once more evaporate. Precipitation comes in various forms such as rain, snow, sleet, ice pellets, dew, hail, and others. The air is full of water vapor, which condenses into tiny liquid water droplets to form clouds. When the cloud droplets combine to form heavier cloud drops which can no longer "float" in the surrounding air, it can start to rain, snow, and hail. The precipitation may fall into a water body or onto land. It is then dispersed in several ways. The water can adhere to objects on or near the planet surface or it can be carried over and through the land into stream channels, or it may penetrate into the soil, or it may be intercepted by plants. When rainfall is small and infrequent, a high percentage of precipitation is returned to the atmosphere by evaporation.