Get grip on water balance (and keep performance)

[DanielTollenaar]

It's not all bad, but I can get huge balance errors on the RWS-HWS model; below all > 1%, but it goes up to order of millions of %. File is here: https://we.tl/t-RnHRQhExmH.

Maybe due to simulation settings (dt=300 secs), maybe its the solver and it may be even inputs, but any way we have'll to get it better.