RO pure water to waste water ratio

Does anyone know what the typical pure water to waste water ratio is on window cleaning systems like the Wash-iT, IPC Hydrocart etc?. I did a basic google search for RO systems and the range are from 1:1 (equal parts…good) to 10:1 (10 being waste water, 1 being pure water….not good)

I think on the Wash-iT, if I understood Perry’s marketing point correctly, this ratio is not fixed because the system does auto-balancing to always provide the correct ratio between waste to pure water.

I’d be very interested to hear from Perry (if he comes across this thread) on how the Wash-iT can achieve this. Unless it’s proprietary info and we’ll just have to take his word for it that it does a good job somehow automagically.

my wash it: 1:1.35 @40psi 7gpm temp in the 70’s input

.4gpm pure water
.54 gpm waste water

I’m sorry, could you be more specific? :wink:

what is waste water? I thought every drop went through the tanks and out the brush…

If you are using a pure water system that includes RO (reverse osmosis) you will have waste water. It’s the nature of how they work. Water passes through a membrane and all the impurities eventually collect and are flushed out while the pure water passes through.

Pure water from a tank is used 100%. But the water had to get purified somehow so it was either from a DI system or combination RO/DI.


As a rule of thumb, most systems are designed to deliver around 30% of inlet water to waste.

The way the Wash-iT does what it does is that, instead of fitting a cheap manual valve with a 1/16" hole drilled in it to set the back-pressure on the membrane, we spend a whole lot more on some tech that another company developed - and we put that in Wash-iT PRO to remove the one thing that can really go wrong - playing with the Reject Valve to change your output of pure (permeate) water has a large potential to damage the RO Membrane.

OK thanks. I was hoping for a little more in-depth technical explanation about this technology to satisfy my curiosity on how it was done automatically, but it looks like I’m not going to get it out of you, which is fine because I respect that it may be proprietary information that you may not want to divulge.

So maybe let me ask the question another way. I notice that for RO system like under-the-sink type, a simple fixed rate flow controller is used to provide a 3:1 to 4:1 ratio. No manual valve is fitted to allow anybody to fiddle around with (and potentially cause damage to the RO membrane). So why can’t this approach be adopted universally with all RO systems for a fool proof design? Why is it necessary to give people a valve to make it adjustable?

Why can’t the Wash-iT just have a fixed flow controller? Why the need for auto balance?

my best guess is because a fixed ro system is dealing with the same incoming pressure all the time, and the same temperature range all the time. my guess is these home-use designed systems are built around an average incoming psi/incoming water temp.

a mobile system that will hook up to a variety of sources at a variety of temperatures needs more adjustability.