All the water on the planet today is the same water that has been here since time began. You drink the same water than Jesus or Mohammed drank. The same water that the dinosaurs drank. This is the same water that your great-great-great-great grandchildren will drink.
How does the water recycle through this process? The water will run through several stages during its cycle.
Evaporation and Transpiration
Most of the water, up to 95%, of all water on earth is stored in the ocean. More is stored in the rivers, lakes and ponds. As the sun heats the surface water, the water will evaporate into vapor and rise into the sky. Some water vapor is also released from plants to help the process.
Condensation and Precipitation
As the air cools, it will condense into droplets and form clouds and fog. When the clouds get heavy with water moisture, it will fall to earth again as rain, snow and hail. Most of this, about 90%, will fall right back into the ocean or on rivers, lakes and such. They will start right back into the Evaporation part of the cycle.
If the water falls on land, it will begin to collect and makes its way back to the ocean. It may go right back into the ocean in the form of runoff. It may infiltrate the earth and collect in underground rivers. It may fall on glaciers or icecaps, and gather and move slowly to the ocean. If it falls as snow or ice, it may sublimate directly to water vapor and start the condensation cycle right away.
As the water flows through the cycles, it may stay in some of the stages for a long time. Some water can take 10,000 years to cycle through the earth. Some water in Antarctica has been dated at 800,000 years, although glacier ice usually cycles in about 20-100 years. In the atmosphere, it will stay about 9 days.
This is all a careful cycle that recycles our water for us. Human interaction can change the cycle. When we cut forests, or pump underground water, we interrupt the cycle. Urbanization of the planet reduces the water that will be absorbed into the earth, and will cut the amount of underground water. If a city is then dependent on that underground water, it may be pumped dry faster than it can be replaced.
The climate can be affected as we affect the water cycle. Ocean evaporation results in cooling of the atmosphere. If we are able to make more water evaporation takes place, this may which will cool the earth. But as more water vapor is in the air, and more clouds form, more solar radiation may heat the atmosphere. There are too many variables here to track.
Water runoff and infiltration will also pickup elements from the ground. In some cases, where lots of fertilization has taken place, the effects of the excess nitrogen have resulted in dead areas of the ocean. In 2008, there were 405 dead zones ranging in size from very small to over 70,000 square kilometers. Most notable in the US is the Dead Zone at the mouth of the Mississippi. It is the size of the state of New Jersey and affects the shrimp harvests of the area.
The water cycle is essential to human life on this planet. It controls the climate on the planet, and enables us to grow the food we need to sustain life. Upsetting the water cycle can upset the climate in unforeseen ways.