How does the earth maintain a relatively constant amount of water?

because of the temperature of other sources

because of the temperature of other sources It's the greenhouse effect, The earth's atmosphere will take in the heat of the sun but will keep the UV rays out for the most part. The atmosphere will then hold the heat and the surface will warm up. However, the areas where the sun rarely shines doesn't warm up, but stays at a cold temperature. The polar ice cap and Antarctica are the best examples. There are times when the area will warm up melting some of the ice. It comes to pass by the sun coming closer and more visible to the location. This is also when the penguins will start to arrive.