You need to prepare :

raw potato

a spoon

salt

How to make it :

Use your spoon to make  a hole in the raw potato. Then put a spoonful of salt in the hole. Just leave it until the next day…and……….

The next day you will see that the hole will full of water!

WHY????

The reason is because potato contains a lot of water, and the salt helped make some of it come out..so you can see it.