potable water

• potable water is water you can drink. has been treated or naturally safe. essential
• potable water is not pure. pure water only contains H2O molecules. potable water contains lots of other dissolved substances
• the dissolved salts are not too high, has the pH between 6.5 and 8.5 and no bacteria or microbes in there
• rainwater is fresh water. this is water that doesn't not have much dissolved in it
• when it rains, water can collect as surface water or as groundwater (in rocks called aquifers that trap water underground)
• surface water dries up, so in warm areas most of their water comes from underground. water from these fresh water sources still need to be treated to make it safe
• to make fresh water safe, you can use filtration or sterilisation
• filtration is a wire mesh that screens out large twigs and then gravel and sand beds filter out any other solid bits
• sterilisation is when the water is sterilised to kill any harmful bacteria or microbes. done by bubbling chlorine gas through it or using ozone or ultraviolet light
• in some areas there is not enough surface or ground water, so instead sea water is treated by desalination to provide potable water - heating the water for fresh water to evaporate and separate from the salt
• sea water can also be treated by a process that use membranes - like reverse osmosis. salty water is passed through a membrane that only allows water molecules to pass. ion any larger are trapped by the membrane. both this and distillation require lots of energy and are expensive, not practical for large amounts of water