Reverse Osmosis - Whole RV or Drinking water only?

Many people want RO water for drinking because it is the best, pure and simple.   It is even better than bottled water, because you don't have microplastics in the water.  You also don't have sediment, nitrates, arsenic, metals, chlorine, or ANYTHING except H2O in the water.   An effective RO system can get the parts per million down near zero.    You can get it by filling your water jugs at the store and carrying it with you OR you can make it yourself as long as you have a source for the water.   There are some considerations you should know before you make the choice to make it yourself

How Is RO Water produced?

RO water is produced by pushing water through a membrane that is so fine that it removes even dissolved minerals from the water.    To do this, you need a flow restrictor on the output of the housing that the membrane sits in to provide back pressure.   This restrictor and the membrane must be the same gallons/day so the pressure is correct for the type of membrane.    Booster pumps are often used to insure that the incoming pressure is high enough to maximize the output of the system.

Pre-Filters

Water should be filtered for sediment and chlorine before going into the RO membrane.   Failure to pre-filter the water may lead to the membrane getting plugged or damaged by chemicals.   A dual canister system is ideal for this.

Efficiency

2 to 3 times as much water is discarded than is converted into RO water.   That means that, if you fill a 100 gallon tank with RO water, 200-300 gallons will be discarded down the drain.   Some RV parks don't allow filling your tank with RO water due to the low efficiency... that is if they catch you!

Using RO water in an RV

RO water generation is so slow, measured in gallons per DAY, that you can only use it by storing the RO water in a tank and then either pressurizing the tank or pumping the water into your plumbing from your fresh water tank using your RV pump.   There are two types of RO systems - Whole RV or Drinking water Systems.

Whole RV RO

This is where you generate RO water and store it in your on board tank.   It can take a day or two to fill up a 100 gallon tank with a 75 gallon/day system, while discarding 200-300 gallons of water.   There is nothing wrong with this water, as it is already filtered through sediment and carbon filters, but it does go back into the sewer or water system or out onto the ground to water plants.   

After the tank is full of RO water, the water is devoid of minerals, so it has a low pH, which means it is acidic.   Acidic water is a VERY good solvent, and can damage small metal parts in tankless water heaters.  To avoid damage, you may need to add a small amount of minerals back into the water before putting it in the tank.   We have a Mineral Adder for this purpose. 

To maximize efficiency, a booster pump may be put between the pre-filters and the RO Membrane housing.   These pumps have about 70-80 PSI and are on whenever power is applied.   Without the pump, you will be running the system at 40-60 PSI, and production will be slower.

You can choose to automate your whole RV RO system so that it comes on when the water level in the tank drops below a set level, then turns off when it is full.   A tank level controller will control the power to the boost pump and turn the availability of source water on and off based on the sensors installed in the tank.

Drinking Water RO Systems

Drinking water RO is only in one location, usually under the sink.   You would pre-filter the water coming into the RV, then put only the RO portion under the sink.   The flow is still slow, so you need a small tank, usually 2-4 gallons that holds the water.   As the water fills the tank, it builds pressure up in the tank.   This pressure is measured and compared to the source water pressure with an automatic shutoff valve.   When the pressure gets to 60% of the source pressure, the valve shuts off the source water, and the system reaches equilibrium

 This system uses a separate faucet installed by the sink to dispense the water.   When the pressure is released, the auto shutoff valve allows the source water to flow and refill the tank.   

Since there is a small amount of water being processed at a time, you can choose to either put the brine water down the drain, or, if you are dry camping (boondocking) you can choose to put it back into your main holding tank for reprocessing.    While it is slightly (about 25%) more concentrated than the source water, it won't be a problem as long as you are using your tank for showering, washing dishes, flushing toilets etc as well as generating the drinking water.  We have a Boondocker option for this use.