RO/DI unit: Soft or hard water?

[Todd]

I just bought an RO/DI filter, but have not received it yet. I was wondering do I hook it up to my water before or after my water softener. I don't want to use softened water for the aquarium, do I?

 

[lando]

I have mine filtering hard water. Using soft water just gives the filter more to remove and will decrease the life. Plus, for every gal. produced by the RO/DI there is over four or five gals of waste water. No need to waste all of that soft water.

 

[OneBowl]

Agree with lando. Hook it up to the untreated source line. An additional benefit will be that the waste water can be used for a garden, whereas the briny waste water from the treated line would not be good for plants. Would further recommend that you discharge away from a septic system, if you have one and if possible.