R/O unit 3rd canister not filling??

I have a small 60 gpd r/o-di unit and the third canister ( the DI I think ) never fills up with water since I bought it, any ideas?

 

I have a spectrapure unit and it's normal for the di (3rd filter) not to fill up,I can see water trickle down the clear casing out of the ro membrane,but the water pressure pushes it up through the bottom of the center of the di filter,completely normal providing you have 0 tds coming out at approx a 4 to 1 wasterwater/ro/di ratio.

 

Good to know thanks

 

Same here as grinder's.

 

Same for me.

 

That is entirely normal. The sediment and carbon canisters are under house pressure so fill all the way. Once it leaves the RO membrane it is basically atmospheric pressure since the discharge line is open so it only fills part way. Hold your finger over the end of the treated water line or raise it over your head and it fills higher, lower the to the floor and it drains lower. Normal and not a problem.