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How To Buy a Whole House Reverse Osmosis(RO)
System
Once you have decided that you would like to purchase an
RO system that will produce all the water in the house, you will need to answer the following questions-
How much water do I need?
To size an RO you must first determine your water requirements.
Most people use between 50 and 75 gallons or water per day. This includes drinking, food preparation, cleaning,
clothes washing, toilets, showers etc. We recommend you choose the higher number (75 gallons per day per person) for
sizing the system. We also recommend you consider by-passing the clothes washer and toilets if possible to conserve
water.
Example – A family of four will need to have 4 X 75 = 300
gallons per day.
How much storage should I have?
Because RO systems typically produce water at a rate slower
than it is used, the RO will need to run even during times of no water usage. The water it produces needs to be
sent to a storage tank for use at a later time. The storage tank should be at least as large as ½ of your
daily household consumption. This will allow for peak uses during the morning and evening. We recommend that you size the tank for one day's storage.
How large an RO do I need?
Reverse Osmosis units are expensive and therefore it is important
not to oversize the unit. At the same time, if the unit is too small, it will have to run all the time and will
wear out prematurely. We recommend that the RO be sized
so that it need not run more than about 8 hours per day
to produce the water you need. This sizing will reduce wear and tear on the pump and motors, provide for unexpected
peaks and allow for increased future demand.
There are number of factors that affect the output of an
RO. You should be aware that the rated output of the RO is seldom the actual output in the field. Cold water and
high salt content will be the most common reasons for this reduced output. Have the person selling the RO tell
you what the actual output will be under the conditions your RO will be operating.
What features should the RO have?
Large RO’s tend to have more standard features and options.
Standard features on whole house RO usually include-
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- Liquid filled system operating pressure gauge
- 5 micron cartridge pre-filter
- Solenoid feed water shut-off
- Adjustable system pressure regulator
Typical required options available ( in order of importance)-
- Pre-filter pressure gauges
- Low pressure cut off switch
- Recycle valve
- Flow meters for permeate(treated water) and reject(waste
water)
- Pretreatment lock out control
- Permeate quality monitor
- Permeate flush
Pre-filter pressure gauges-
will allow you to monitor the pressure change as the water passes through the pre-filter. A large difference in
pressure indicates a dirty filter. If the filter is not changed, before it becomes too dirty, the RO will shut
down or be damaged.
A low pressure cut off switch- is essential to prevent damage to the RO pressure pump. This switch will turn
the RO off if there is not enough water provided to the RO pump. There are two general types of switches used to
do this-
- The first type automatically resets itself when water pressure
returns. This type can cause damage to the pump if the shut down was caused by a dirty pre-filter. A dirty pre-filter
in this type of system will cause the RO pump to cycle on and off rapidly and over heat.
- The second type will not reset itself or will only reset
after an extended period of time(typically minutes or hours). This type of switch will prevent damage to the RO
pump even if the pre-filter is the cause of the low pressure condition.
A recycle valve-
will reduce water waste. An RO that does not have a recycle valve will waste 4-5 gallons of water for every gallon
of water produced. With a recycle valve, this waste can easily be reduced to 1 or less gallons of water wasted
for every gallon of water produced.
Flow meters-
will allow you to monitor RO performance and adjust the efficiency.
Permeate quality monitor-
will allow you to determine if there is any deterioration in performance of the RO.
Pretreatment lockout-
shuts the RO down when the pretreatment equipment is regenerating. Most pretreatment equipment by-passes raw water
during the regeneration process. Shutting the RO down during regeneration will prevent untreated water from reaching
the membrane.
Permeate flush-
will help reduce mineral build up on the surface of the membrane and reduce start up TDS spikes that reduce the
overall quality of the water. This is essential on systems with a recycle valve installed. Flushing also increases
the life of the membrane.
Although typically offered as options- pre-filter pressure gauges, a low pressure cut off switch and a recycle valve
are essential on all whole house systems. We also
recommend flow meters
and a permeate quality
monitor for all systems.
Should I put the reject (waste) water into the septic
system?
Most of the time the amount of water that is produced will
overburden your waste water system. We recommend that you send the water to a dry well or out the basement drain
system if it will handle it. In many cases, this water can also be used for irrigation.
What provisions are made for disinfecting the storage
tanks and stored water?
Many times people will us UV(ultraviolet) lights on the water
that is pumped from the storage tank. At a minimum, the tanks need to be sanitized at start up and need to have
chlorine(household bleach) added periodically to maintain disinfection.
Is RO water corrosive and if it is what can be done to
treat it?
If water has all of the minerals removed, it can become corrosive.
This is usually only a problem with ultra pure water(all minerals removed) and not with RO water. However, if this
becomes a problem, it usually can be corrected with a calcite contactor. The contactor is a tank filled with limestone
chips that will dissolve into the water and make it less corrosive.
How much will a system Cost?
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Item
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Cost
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| Pretreatment(if required) |
$1600-$2800
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| RO (rated at 1500 gallons per day, TDS <2000ppm) |
$4000- $5000
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| Repressurization (pump system to deliver water from storage |
$575
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| Storage Tanks (cost per 150 gallons) |
$300
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| Disinfection (Ultraviolet light) |
$1595
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| Calcite contactor (if necessary) |
$1295
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