1
Get a large pot with a lid and an empty drinking cup. The glass should be big enough to hold a fair amount of fresh water.
Make sure the glass is short enough that you can still put the lid on the pot.
A Pyrex or metal cup is safest, as certain types of glass will explode when exposed to heat. Plastic may melt or deform.
Make sure the pot and lid are suitable for using on a stove.
2
Slowly pour some salt water into the pot. Do not overfill.
Stop well before the water level has reached the mouth of the glass.
This will make sure no salt water splashes into the glass while boiling.
You don't want to get any salt water into the drinking glass, or your newly made fresh water will be contaminated.
3
Place the pot cover upside down on the pot. This will allow the water vapor as it condenses to drip into the drinking glass.
Position the pot lid so the highest point or handle is facing down directly above the glass.
Make sure the pot lid is providing a good seal along the edges of the pot.
Without a good seal, a lot of the steam will escape and diminish the supply of fresh water vapor.
4
Bring the water to a slow boil. You will want to boil the water slowly over low heat.
A violent full boil can contaminate the drinking water by splashing into the glass.
Too much heat can cause a glass to break.
If the water is boiling quickly and violently, the glass may shift away from the center of the pot and the handle of the pot lid
5
Watch the pot as the water condenses. When water boils, it becomes pure vapour, leaving behind anything that was dissolved in it.
As the water becomes vapour, it condenses in the air as steam and on the cover's surface as water droplets.
The droplets then run down to the lowest point (the handle) and drip right into the glass. #*This will probably take 20 minutes or more.
6
Wait a little while before drinking the water. The glass and water will be very hot.
There may be a small amount of salt water left in the pot, so be careful when removing the glass of fresh water not to splash any salt water into your fresh water.
You might find that the glass and fresh water will cool faster if you remove it from the pot.
Be careful as you remove the glass so you don't get burnt. Use an oven mitt or pot holder to take it out.