understand what RO accomplishes RO FILTRATION

[hitman inc.]

Hello,
I understand what RO filtration accomplishes but I'm trying to figure out when?
Is this a process employed when filtering water prior to adding salt, and then adding the mixture to the tank?
Thanks!

 

[dreeves]

Prior to adding salt.

 

[broomer5]

... and for all evaporated top off water too.
Filling the tank initially with RO water is a big plus as well.