The total amount of water on planet Earth has remained constant for nearly 4 and a half billion years. Hardly any leaks off into space – but we need to be careful with it.

It is now estimated we have over 3,000,000,000,000,000,000 gallons of it, dispersed not only in oceans, rivers and lakes but also under the ground as well as in the air and clouds. This amount of water is kept constant due the continuous water (or hydrologic) cycle of the earth. As rain falls, it fills the lakes and rivers which flow into the sea where it evaporates into the air as water vapour, forms into clouds and deposits it back again as rainfall.

Oceans contain about 98% of the total amount of water on earth, with 1.6% of the remaining 2% being locked up in the polar ice caps and glaciers. About 0.36% of the remaining 0.4% is out of sight locked away in aquifer rocks and reservoirs, and 0.01% is actually in the air and clouds leaving just 0.03% in our lakes, rivers and reservoirs.

The problem for humans is that most of our water is saline and is of little use to us. Marine life depends on salt water to survive so humans must not intervene too much. The reason for the sea’s salinity in the first place is that the Earths’ rocks contain sodium and chlorine ions which are collected by the acidic rain (rain that has absorbed some carbon from the atmosphere) and then eventually washed into the sea. In addition to the sodium chloride added to the oceans in this way, the sea beds are continually producing salt via underwater eruptions. Luckily for us, evaporated sea water vapour leaves the salt behind thus the sea remains saline, and may actually be getting more salty. The sea does, however, get rid of a lot of its salt due to the millions of sea creatures that absorb it and after they die, there bones and shells finish up on the sea bed as sediment. Eventually this sediment turns into rock and, where it has risen above sea level over millions of years, this sedimentary rock – in particular limestone – gets absorbed by rainwater and is eventually washed back into the sea.

There is currently a worldwide problem with fresh water shortages due to general wastage, increased agriculture and the rise in population – It may surprise some that the average human in the western hemisphere uses over 30 gallons of water every day. Desalination plants would appear to offer some answer to water shortages but whilst they produce some 0.3% of the Earths’ fresh water supply, they are simply not energy efficient at the moment.

The big problem for life dependent on both fresh water and salt water is of course pollution, and whilst the Earths’ water remains constant, its quality is quite another matter. Pollution of the world’s water supply from industrial processes and agriculture is a problem that needs to be resolved soon – and quickly.