I need to write a procedure for putting DI on line in the event of our main RO failing. I seem to remember reading somewhere that the softener should be by-passed when using DI as the only purification system. I have a gambro c.w.p. and I cant find it in my manual. Any in-put would be greatly appreciated.

yes the softener has to be bypassed due to sodium causing the DI to be used up faster and getting in the water.

I also have a CWP and yes, you need to bypass the softener when you are running on D.I.

I think this is the thread your looking for.
water softener conversion
Not sure which way to go with this one.
I nominate Chuck, as a neutral third party, to do an experiment of exhausting DI with & without the softener and report back with the findings! J/K
It would be interesting though, but I doubt anyone has the spare time or money for this.

The link provided by B is where this was discussed before. As I mention in that link, it does not make any difference if the Softener is bypassed or not. The calcium and magnesium in hard water will take up the exact amount of capacity on the DI resin as the Sodium would have taken up if the water was run through a Softener first. DI will remove 99.99+% of the sodium in the water. If it didn't, you would not get 18 Mohm water on the effluent of the DI. Technically, DI will remove Ca and Mg slightly more efficient, but you will not be able to measure the difference.

If you want to bypass the softener, that is acceptable. If you don't want to bypass the softener, that is acceptable also. The DI will produce 18 Mohm water either way.