Loading... Please wait...

Our Newsletter

The Right R.O. System


R.O. Basics

All R.O. systems operate on the same basic principles.  They all take water containing minerals and run it through a membrane cartridge that separates the water into product water that has most (up to 99%) of the minerals removed and waste water that contains the minerals that have been “rejected”. 

 First, R.O. systems need water under pressure to push pure water across membrane material while holding minerals behind.  The more pressure the more water is produced and the higher % rejection of minerals.  City tap water is a steady 55-65 psi and is easy to work with whereas water from private wells cycles between two set points and presents more problems for R.O. systems.

 Second, R.O. systems need water that is free of particulate matter and TFC based systems (98% of the systems on the market today) must have the chlorine found in tap water removed.  A separate 5 micron prefilter can remove particulate matter while the carbon prefilter removes chlorine.  In our MT line models a single 5 micron rated matrix carbon block prefilter removes both in a single combined prefilter.

 Third, water temperature will affect R.O. efficiency.  Lower water temperature makes water more viscous (thicker) and impedes water movement across the membrane.  As a result customers with cold winters will get less product water when it is coldest.  Again, private wells tend to have colder water and lower production.  (Never try to improve your R.O. efficiency by mixing hot and cold water from your faucet as this produces “spikes” of hot water that can destroy your membrane.)


To Tank or Not to Tank

 Most of our customers do “bulk processing”.  In other words, they hook up their R.O. to a coldwater source, make a batch of water they collect in a reservoir (jug or trash can or barrel) and then turn the water off.  This works well if you are filling aquaria or doing water changes with fish.  It also works well if you are simply watering your plants.  We offer several devices that automatically shut off the water when the collecting reservoir is full.  We refer to the reservoir as an atmospheric setup as there is no additional pressure provided to deliver the water outward.  Some customers mount the reservoir high up in their setup and use gravity to deliver the water.  Others use a pump while still others simply dip in to fill smaller containers and remove water.

 When you need pressure to run a mister or humidifier, an atmospheric setup presents challenges.  Automation can use solenoids to trigger pumps that deliver water under pressure but the complexity puts off those without engineering degrees.  A far simpler solution is to use a system with a built in shutoff device and a bladder tank that stores water under pressure.  Basically, a bladder tank is half water reservoir sitting on a rubber gas-filled bladder that is depressed as the tank fills with water.  When the tank is full, the R.O. system shuts down.  When your mister or humidifier needs water, the tank delivers water under pressure as the gas bladder pushes the water out at 11 psi, enough to run either device.  As the tank delivers water, the R.O. turns back on and refills the tank.  Our most popular system is a 150 gpd R.O. system (that’s 6 gallons/hr.) paired with a 14 gallon storage tank in an orchid greenhouse.  Even when the R.O. is used for watering plants, the 6 gallon/hour refill rate is usually sufficient to keep up with demand.  If it is not we can provide a second 14 gallon tank or go up to a 22 gallon tank.  (If this approach sounds familiar, the typical homeowner system has these features but the production rate is on 24-50 gallons/day and the bladder tank only holds about 2 gallons.  We sell these as well.)


CTA versus TFC membranes

 This was a major question back in 1986 when we began our business.  Since then CTA membranes have fallen out of favor and TFC dominates the market.  Does this mean that a CTA membrane is always inferior?  Not at all!  It is just more limited as to when it can be used.  First, your hardness cannot be extreme as CTA membranes need a feed water of less than 300 ppm or about 16 DH.  They are also based on cellulose that can be digested by bacteria so they need a chlorinated water supply to kill the bacteria.  This rules them out for wells.  Membrane life tends to be shorter although I have seen CTA membranes last 5 years.  Finally, the only reject 93-94% of the minerals in water versus 98-99% for a TFC membrane unit so they are not suitable where ultra-pure water is the goal.  As a result they are not made in larger sizes nor are the found in higher end systems.

 So when is a CTA membrane a good idea?  We have customers in San Francisco and other soft water areas (their snow melt water from the Hetch-Hetchy reservoir rarely tops 80 ppm) who bulk process small amounts of water for several aquaria or a few orchids who love these systems.  These systems don’t have carbon prefilters so there is really nothing to change until the membrane fails.  They are the “Model T” of R.O. units and we still sell and support them.