On default settings:

Producing 100 units of pure water by burning hydrogen and oxygen in Chemical Plant 1 takes around 1.14 seconds with around 294 kJ energy consumption.

On the other hand, producing 100 units of pure water plus some saline water in Hydro Plant 1 takes 1 second with 155 kJ energy consumption.

This implies that one is better off discarding all the hydrogen and oxygen byproducts and processing new water from scratch than redirecting them into chemical plants and making use of the byproducts. The reaction itself is exothermic and self sustaining to begin with, yet it's somehow more electrically expensive and takes even longer to complete compared to processing water from a new source with hydro plants ? I believe this recipe needs a bit tweaking as it also strongly discourages byproduct utilization.