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Old 04-29-2011, 12:28 PM   #1
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Join Date: Aug 2010
Location: North Texas
Posts: 991
Thumbs up Reverse Osmosis Drinking Water Unit

I guess it goes without saying, but we all probably worry about water quality when we hook up at certain campgrounds or potable water fill locations. One experience many years ago at a National Monument campground in New Mexico taught my DW and me to always be aware of what's in the water. That's probably the reason we decided to spend the money now while our fiver is still new and install a Reverse Osmosis drinking water unit.

I did research reverse osmosis units for RVs for a couple of weeks and decided on a system from The RV Water Filter Store (www.rvwaterfilterstore.com). Several reasons drove this decision: the owners are full-timers themselves, the compactness of the unit, and the "Boondocker Option". There were two different types of units to choose: Whole RV System and Drinking Water RV System. Of these options, one could get a basic system which omits two pre-filters or a regular system. The basic system is less expensive and takes up less space, but one needs to be sure to have a good filtering system for incoming water (such as a 5 micron to 1 micron filter). Even though I do have an excellent filter on the fiver for incoming water, I opted for the regular system that included a 5 micron filter and a secondary 1 micron filter. Yes, it is overkill on filtering.

So, the Regular System consists of three filter tanks: 5 micron -> 1 micron -> charcoal that feed the water into the reverse osmosis membrane unit located on top of the filter tank bracket. And additional "finish charcoal filter" is attached to the membrane unit and gives that final filter touch to the RO water as it is drawn from the unit or reserve tank. I also purchased the 12 volt pressure assist pump with pressure on/off switch, a permeate pump, and a 3 gallon pressurized reserve tank. The RO process works by pressure difference across a semi-permeable membrane. The 12 volt pressure assist pump will assure that the system will work independent of the plumbing pressure of the RV. The permeate pump runs by the output "brine" water from the membrane unit and pressurizes the RO permeate (the "good" water) going to the reserve tank and the delivery faucet. The permeate pump also lowers pressure on the "good water" side of the membrane unit, so it ups the efficiency of the system. The 3 gallon reserve tank holds basically 2 gallons of reserve water inside a collapsible bladder sealed inside the larger tank (thus giving water pressure).

In the Alpine 3640RL, the kitchen is contained on a slide extension, so the fresh water lines and the sewer lines have flexible hose parts at the base of the sink unit. I measured the length of the filter unit beneath the bracket mountings, added a couple of inches, and marked the top and bottom where a brace board would be placed for this bracket. Forward of this sink area is a "hidden" canned goods drawer that is within the wall of the slide. I released the rails on this drawer and removed it temporarily. I drilled two holes each side into the 1"x2" side wall frame between the under-sink and the drawer area. Via measurements, I placed a backing board in the drawer area and got my DW to hold it in place while I marked through the drill holes. I joined the brace board and the backer boards with carriage bolts and wing-nuts. I held the filter unit up to assure it cleared the flexible piping and marked the mounting screw points on the brace board. I then removed the filter units including the permeable membrane unit for easier installation. Once the bracket was mounted, the filter units were once again installed and checked for clearance of the flexible piping.

I removed the drinking water faucet installed by Keystone and replaced it with the larger faucet that came with RO unit. I also mounted the finish filter to the side of the RO filter unit (rather than leaving it on top) on an extended side of the brace board.

In the Alpine 3640RL, there is an access area next to the stairs under the pantry. Earlier I had re-routed the fresh water fill line to correct a kinked line problem, so there was more than enough room to install the reserve tank in this area. I mounted eyescrews into the back wall and looped a small webstrap through them. I attached foam insulating tape to the back of the tank to prevent it from rubbing the wall, placed the tank in the access area, and secured it with the webstraps. There was also space to install the 12 volt pressure assist pump. I was careful to leave enough slack in the connecting water lines to allow for the movement of the kitchen slide. I put the on/off pressure switch on the line to the reserve tank.

The permeate pump mounting came next. I closed the slide (and checked for connecting water line binding) and marked where the flexible sewer line was located. The slide was extended and the permeate pump was located beneath the travel of the sewer line.

As Keystone had provided a cold water connection for filtered drinking water, I utilized that connection with some parts from Home Depot and connected the feed water line with a valve.

I disconnected the 50 amp power from the fiver and disconnected the batteries. I removed the front from the power panel and connected a 25' white primary wire to the bottom fused connector and a 25' black primary wire to the grounding connector. I paired these wires together with small cable ties and fed about 3 feet through the wiring access hole at the back of the power panel. Inside the upper utility basement, I used a coat hanger hook to catch those wires and feed them across to the other side of the basement to the access port. These wires were pulled through and enough slack left to allow for slide movement. I drilled a hole beneath the sink on the front panel and mounted a 12 volt switch I purchased from a local auto parts store. That switch was then wired to the pressure switch and the pump in series. Thus with the 12 volt switch "off", the RO system is off.

The "Boondocker Option" was last. From the brine output of the permeate pump, I connected a T and two valves for the brine output. One line led from the valve to the gray water vent pipe contained within the access area beneath the pantry. The supplied saddle connection was used to connect this line to the gray water tank. The other line was run back out to the upper utility basement area and to the back of the WaterWorks. I utilized a 1" nylon polypipe splice with a quarter inch hole drilled at its midpoint. I stuck the brine line into this hole and sealed it profusely with silicon caulk. After the caulk had set, I cut the fresh water line and spliced it back together with the modified splice.


To produce RO water while traveling or while boondocking, we just have to leave the fresh water pump on and turn the RO system on. The pressure assist pump will assure that there is enough pressure within the RO filter unit to drive it. The valves can be turned to return the brine water (which is still good water for bathing, etc.) to the fresh water fill line.

When camped and connected to "city water", we have two options. One option is to dump the brine water into the gray water tank. The other option is to use the brine water to "fill" the fresh water tank for use while we are traveling or boondocking. Recycling at its best!

Note: For every gallon of "good" RO water produced, three to four gallons of brine will be output. There is actually nothing wrong with this brine (given it was "good" potable water in the first place) that it cannot be used for bathing, washing, etc. I would suppose that if one allowed this brine to be used and recirculated back to the fresh water tank to be used again and again to produce RO water, sooner or later one might get a harmful concentration in the brine. But that's a little extreme, don't you think?

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