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		RO and DI Water Filters Information
		Randal Bogarth	November 1, 2002
		R/O and DI water are simply water that has been passed through 2 completely different types of filter. An R/O unit uses a purely mechanical (Molecular/atomic) type of filtration to filter larger molecules through a semi-permiable membrane. The Membrane has holes in it that are in the 400 AMU (Atomic mass units) range in size. This is why some organic chemicals and lighter compounds such as N03 and NH3 pass through the membrane more than larger elements. DI water is water that has been passed through a chemical filtration process, using a Deionization resin. Generally for water filtration applications a mixed bed of Cation and anion resins are used to trap both positive and negative charged ions. Water passing through the resin leaves it's ionic content chemically bound inside the resin. R/O water treated with DI at the proper flow rate should have 0 dissolved solids (TDS). R/O water itself coming from a 4 or 5 stage R/O unit should have between 4-20 TDS ballpark. That number is highly dependent on the conditions that the membrane is operating in. (Water temp,pressure,PH, dissolved solid content) DI only treated water can have just about any amount of TDS depending on your water conditions, the size of the DI unit and the flow rate of the water going through it. DI is not as efficent at removing all material in water by itself but will trap some of the ions in its resin regardless of operating conditions thereby providing some water softening effect. If your flow rate is higher than the specifications, some of the Ions will pass. DOW chemical reccomends a very deep bed of resin to completely DI water, to the point of being impractical for home use. As far as fouling membranes goes, hard water with Calcium,Magnesium and Iron will foul membranes faster than water that is "Hard" because of sodium or other dissolved Ions. Simply remove the flow restrictor from the waste line and let the unit run free for 10 minutes or so and you have flushed your membrane and greatly reduced the fouling. Put the restrictor back and you're back in business. To check the effectiveness of your membrane, use a TDS meter (Robert, this is probably what your R/O unit has built in) and keep track of how much product water you are producing. If your TDS rises and your product water decreases, Check your prefilters or replace them (should be repaced every 6 months regardless). If the TDS is still high,Product low, check your water pressure. If this is still consistant (shower feels the same as always, faucet is putting out the same water pressure) more than likely it is your membrane. Be advised that in the winter, cooler feed water will decrease membrane efficiency and make the TDS go up slightly and the product decrease. This is not a problem with the membrane it is just the way it works. A membrane failure will indicate with either creeping TDS (Gradual increase)over a short period of time, or a dramatic increase in TDS. Check your product water weekly with a meter and you should have no problem ID'ing problems before they get serious. Just remember to check your prefilters before chucking a membrane. DOW carries a 2 year warranty on their Filmtec membranes provided you have the proper prefiltration. The membrane can also be inspected for fouling by gently removing it from the housing and gently squeezing it. If it makes a crackling sound it is fouled. While you have it out, smell it. If it has a foul odor, it is bacterially fouled and should be replaced. I personally replace the membranes yearly just to be safe in the bacterial areas.

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