I use a valve on waste water to prevent back flow, but not limit the output. Then I put a valve on fresh water to limit its input to the amount needed minus waste water output. It does take a little to get up to 100%, but I haven’t had any issues lately.
I’m sure you’ve done this, but you’ll want to make sure you’re using all of the water being input based on calculations.
For instance, if you’re making 100 m3/min and you need 400 m3/min for 100%. Then you’ll need to limit fresh intake to 300 m3/min. However, if your refineries aren’t running at 100% and maybe only using 300 m3/min then your waste won’t be used to full capacity.
To counter this I tend to starve the system of water by limiting fresh and then bumping it up until max is reached.
It’s a bit finicky, but seems to work for me.