If you're wondering what sort of pressure the water companies might have put on Labour to rule nationalisation out of the new water commission's remit, my guess would be it would be related to the problems of Investor State Dispute Settlement.....
and if you not sure what that entails, here is a piece I wrote for @NWBylines a while back setting it out....
I may be wrong, but it feels like a plausible explanation for the commission's limited terms of reference!