C14.2 Water safe to drink Flashcards
What is potable water?
➢ Water that is safe to drink
Why does water become impure?
➢ Rainwater dissolves some gases from the air as it falls to the ground
What happens when the water first gets filtered?
➢ Water is passed through a special filter made of fine sand gravel.
➢ Removes any remaining particles of mud or
grit
What happens after the water passes through the water filter?
➢ Water enters the water treatment works
➢ Passes through a screen that is made from bars of metal placed close together
➢ Removes large objects such as leaves and twigs
What happens after it enters the water treatment works?
➢ Water is transferred to a settlement tank - where the sand and soil settle out
➢ Aluminium sulfate and lime are added to the water
➢ Small particles of dirt clump together so they sink to the bottom of the water
What happens after Aluminium sulfate and lime is added?
➢ A small amount of chlorine is added to kill any bacteria or microorganisms
➢ Alternatively ozone can be added or UV light used
What happens after chlorine is added?
➢ pH of the water is checked and corrected so that it is neutral
➢ It then is stored in large tanks and service reservoirs ready to be pumped to homes or schools etc
Why do some places have to use seawater as a source of water?
➢ Because in a drier climate there is a lack of water
Why is distillation expensive?
➢ Because of the energy costs involved in boiling large volumes of water
What is flash distillation?
➢ When water is under reduced water
➢ This reduces the boiling point
➢ Making it cheaper
What is desalination?
➢ Converting salty water to potable - useable water
What is reverse osmosis?
➢ Uses the membranes to separate the water and salts dissolved in it
➢ No heating involved so uses less energy than distillation
➢ Energy is still needed to pressurise the water passing through
➢ Corrosion of pumps by salty water is also a problem
What is the test for chlorine gas?
➢ Damp blue litmus paper
➢ It is bleached if chlorine is present
