What will happen if fresh water and salt water mix together?

What happens when fresh water and salt water mix is that they would form layers because salt water is heavier.

Will we ever run out of water?

Yes, it is told by many scientists that we will run out of water sometime in the future. That is because humans are polluting our fresh water supply.

How many water droplets are in a cloud?
The amount of water droplets in a cloud is no different than the amount of water droplets in the atmosphere. It also depends on the size of the cloud. That being said you can not measure it.               

What temperature does water freeze at?

Water freezes at exactly 32°

Are clouds made of just water?

Yes, clouds are miniature droplets of water or ice crystals in a big bunch. Also they are water molecules.