Get the salt

Students are given some dirty salt (salt +sand/soil..whatever you wish) I have even simulated urine(orange juice) to reinforce the plight of poor hygeine in some countries.
The sheet takes students through the 3 steps of purifying the salt.
The final step of evaporating the water using evaporating basins can be tricky if the heat is left on too long.....if no bunsens/heat is available you can just leave the solutions to "dry out" naturally..you can get nice crystals forming over a couple of days.
Why not take the students out for fish and chips later on (keeping a sample of your salt to sprinkle on your chips)