Are you not on municipal water? Seems like a lot of fussing around considering Melbourne has great water for brewing once you get the chlorine out.
If you really want to get very consistent results it's hard to hone in the recipe with town water as it varies through the year and the report gives such wide range of values it's not useful. Yes you can probably make good beer but without it with some variation from batch to batch. If you really want to make highly consistent beer RO is really the best option. If any of you guys just find water chemistry too complicated then simply use
Brewfather. This software makes it really easy and
Nathan did a great video on this here. We do give free RO water away at our Distribution Centre at (410 Princes Hwy, Noble Park North) so if you live in the area bring your tanks or whatever and fill them up for free.
Now with your question about putting some type of flow stopper/float switch or something like that to block the output this is not a good idea. When the output of the RO water system is blocked water will continue to flow and get diverted into the drain so this would be a waste of water. You could use the
fill-o-meter on the input side of the RO Water System however you must remember this would measure total water into the filter including the waste water not volume of good RO water collected. This would however be much better than nothing and still be really useful.
If you wanted to go one step further than this then I would recommend getting an inexpensive float switch that looks like this:
Then use a power supply and one of these
inexpensive solenoid valves and then install using this
inexpensive 1/4 water tubing. So put the float switch into the bucket/brewery or vessel you want to fill the use the solenoid valve to turn off the water supply into the RO water system. This will be the most efficient and reliable way to solve the problem but you will need to do some basic wiring yourself.
I should also mention that if you have back pressure into the vessel you are filling up (such as going into a Fermzilla) this will also effect the efficiency of the RO membrane so it's also not a good idea. It's really best to come out of the RO vessel and straight into a bucket or unpressurised container or into the brewery directly. Higher pressure differential into and out of the RO filter will give you better efficiency, faster flow, and reduce waste water.