Thirsty? How 'bout a cool, refreshing cup of seawater?
No, don't take us literally! Humans cannot drink saline water. But, saline water can be made into freshwater,

Desalination, or the removal or salt from water, can be used to produce drinkable water from seawater or brackish water. Scientists are studying ways to use desalination on a global scale, but you can desalinate water yourself with just a mug, a bowl, and some sunlight.

How to Desalinate Water on a Desert Island

Evaporation is the process of a substance in a liquid state changing to a gaseous state due to an increase in temperature and/or pressure. Evaporation is a fundamental part of the water cycle and is constantly occurring throughout nature.

Filtration systems treat water by passing it through beds of granular materials (e.g. sand) that remove and retain contaminants. Conventional, direct, slow sand, and diatomaceous earth filtration systems all do a good job of removing most protozoa, bacteria, and viruses (if coagulation is used). Bag and cartridge filters generally do not remove any viruses and few bacteria

About 780 million people—a tenth of the world’s population—do not have access to clean drinking water. Water laced with contaminants such as bacteria, viruses, lead and arsenic claims millions of lives each year. But an inexpensive device that effectively clears such contaminants from water may help solve this problem.

Water filters have a long history as a method of water purification, beginning as early as 2000 b.c.e. in ancient Egypt. Filtration has evolved from the simple Hippocratic sleeve of ancient Greece, made from cloth, to the complicated solid block carbon and multimedia water filters currently on the market. Water filtration is now the premier method of water purification, removing more water contaminants, more efficiently, than any other technique.

Too much of the world lacks access to clean drinking water. Engineer Michael Pritchard did something about it — inventing the portable Lifesaver filter, which can make the most revolting water drinkable in seconds. An amazing demo from TEDGlobal 2009.

When we turn our taps on, we naturally assume the water is safe to drink. This is because it is treated before it is supplied to our homes. In some parts of the country, fluoride is added to the water supply but this is controversial. Water can also be filtered at home – to help improve its taste and quality. In parts of the world where water is more scarce, sea water is distilled to provide drinking water.

Dissolved Air Flotation (DAF) is another form of clarification process that relies on flotation of floc particles to the surface instead of gravity sedimentation. It is suited to particular quality raw water streams – generally low turbidity, coloured waters which would otherwise be more difficult to treat by sedimentation. The DAF process is also particularly suited to the treatment of nutrient-rich reservoir waters that may contain heavy algal blooms.

Sedimentation is recommended as simple pre-treatment of water prior to application of other purification treatments such as filtration and disinfection methods. It removes undesirable small particulate suspended matters (sand, silt and clay) and some biological contaminants from water under the influence of gravity. The longer the water is sedimented, the more the suspended solids and pathogens will settle to the bottom of the container. Adding special chemicals or some natural coagulants can accelerate sedimentation. Three common chemicals used are aluminium sulphate, polyaluminium chloride (also known as PAC or liquid alum) and ferric sulphate. 'PUR' is a powder product containing both coagulants and disinfectant. Some native plants like prickly pear cactus, Moringa seeds, broad beans and Fava beans have all been traditionally used as natural coagulant to help sediment water in a number of countries in Africa and Latin America.

Sedimentation is the process of depositing sediment. It is a treatment process in which the velocity of the water is lowered below the suspension velocity and the suspended particles settle out of the water due to gravity, centrifugal acceleration or electromagnetism. Sedimentation has been used to treat wastewater for millennia. Most water treatment plants include sedimentation in their treatment processes.

A scientist at Michigan Technological University (MTU) has discovered a simple way to turn muddy water — such as water gathered from rivers, streams and boreholes — into drinkable water by using table salt.

The SODIS method is ideal for treating water for drinking in developing countries. All it requires is sunlight and PET bottles.

Water is essential to human life, and it's no mystery that the sun plays an important role in the water cycle on our planet, as water moves from clouds to rain to rivers, lakes and oceans, and back again. Scientists have discovered several ways to use the sun's energy and the processes of evaporation and condensation to help sanitize water and make it safe to drink.