Reverse Osmosis Water Management

[Ray]

Created to help WaterWitchin, but I thought I'd Nye on a bit, so here's my thoughts:

Pure water is best for orchids. They evolved getting very pure water, whether that be heavy, tropical rains or high-altitude dew.

Reverse osmosis (RO) is a reliable, economical way to provide that, if you do not have sufficient rain collection or snow melt capabilities.

RO, unless you go for a VERY large, costly system, is not an on-demand water supply. A "100 gallon per day" system sounds like a lot, but that's around a cup per minute, and you're not watering much at that rate. Storage of accumulated, purified water is the way around that.

My volume demand is low, so I can produce it a few hours in advance. Most residential systems are supplied with a bladder tank to hold about 3 gallons, but in greenhouse applications where the usage can be quite high on a per-watering basis, it is more common to have an open-air storage tank, connected to the RO system through a float valve.

Small RO systems, like the counter-top one I use, are manually operated. Turn the feed water on, collect the pure volume needed, then turn it off. Residential and grower's systems are typically automated, via the use of a hydraulic cutoff device.

A little bit about RO functioning: water entering the device passes through sediment and carbon filters, then goes into a membrane housing. There, the water flow splits in two: some of the water is pushed through the membrane - only pure water passes, and the rejected dissolved solids are flushed away by the other stream.

Back to the hydraulic cutoff: before water enters the membrane it passes through one side of the cutoff, which is about the size of an egg. The pure water exiting the membrane housing passes through the other side before going to the storage tank.



Assuming the pure water usage is stopped, the bladder tank fills, or in the case of an open-air tank, that fills until the float valve closes. When the back-pressure in that pure water line reaches 2/3 of the incoming water pressure, the cutoff snaps shut, stopping all flow of water to the membrane.