CMS SOM App. H, Tag V200

5.2.7 Reverse osmosis: (alarms)

6.2.7 Reverse osmosis (monitoring)

Reverse osmosis: Reverse osmosis devices shall be equipped with on-line monitors that

allow determination of rejection rates and product water conductivity. The product water

conductivity monitor should activate audible and visual alarms when the product water

conductivity exceeds the preset alarm limit. The audible alarm must be audible in the

patient care area when reverse osmosis is the last chemical purification process in the water

treatment system. Monitors that measure resistivity or TDS may be used in place of

conductivity monitors. [Requirements for reverse osmosis systems in ANSI/AAMI RD52:2004

directs users to ANSI/AAMI RD62:2001, subclause 4.3.7].

5.2.7 Reverse osmosis:

Reverse osmosis: When a reverse osmosis system is the last chemical purification process in

the water treatment system, it [should] include a means to prevent patient exposure to

unsafe product water, such as diversion of the product water to drain, in the event of a

product water conductivity or rejection alarm. [Requirements for reverse osmosis systems in

ANSI/AAMI RD52:2004 directs users to ANSI/AAMI RD62:2001, subclause 4.3.7].

6.2.7 Reverse osmosis:

Reverse osmosis systems should be monitored daily using continuous-reading monitors that

measure product water conductivity (or total dissolved solids (TDS)).

Interpretive Guidance § 494.40(a)

ANSI/AAMI RD52:2004

5.2.7 Reverse osmosis

RO systems should be fitted with a variety of sensors to monitor the system’s performance.

Conductivity or total dissolved solids (TDS) sensors in the feed water and product water streams

are used to monitor the membrane’s ability to remove dissolved inorganic solutes. Flow meters,

usually in the product water and reject water streams, are used to monitor the output of the RO

system. RO systems are also equipped with gauges to monitor pressure at various points

throughout the system. Although not indicative of treated water quality, monitoring flow rates

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and pressures can help ensure the system is operating within the manufacturer’s specifications,

thereby ensuring RO reliability.

6.2.7 Reverse osmosis

Other parameters that must be measured daily include product and reject stream flow rates and

various internal pressures to the extent permitted by RO instrumentation. Although these

parameters are not directly indicative of treated water quality, monitoring them can help ensure

that the system is operating within the manufacturer’s specifications, and thus will aid in

maintaining the performance of the RO membranes.

The measurements can be used to calculate rejection of solutes by the RO membrane and

provide a measure of equipment performance.

Percent rejection is calculated using the following formula:

Rejection (%) = Feed water conductivity-permeate conductivity x 100 Feed water conductivity

Newer RO systems may have a direct reading for percent rejection.

Flow rates can be used to calculate the percent recovery of the RO using the following formula:

Recovery (%) = Permeate water flow rate x 100 Permeate water flow rate + Reject water flow

rate

NOTE: The percent recovery is also known as the “water conversion factor.” The terms are

equivalent if none of the reject water stream is recycled to the feed water stream (see AAMI

5.2.7). If some of the reject water stream is recycled, the equation given above provides a

measure of overall water utilization by the reverse osmosis system, rather than the recovery of

water during a single pass through the membrane module.

Suggested reverse osmosis monitoring guidelines from ANSI/AAMI RD52, Table 4 include:

• Monitor the product water conductivity, total dissolved solids (TDS), or resistivity

and calculated rejection rate according to the manufacturer’s recommendations

(continuous monitors) with a result showing a rejection rate greater than or equal to

the facility set parameter percentage;

• Monitor the product and reject flow rates, and calculate recovery daily (continuous

monitors), with a result showing product water flow rate greater than a facility set

number of gallons per minute (gpm); and recovery rate in the facility set % range.

Additional Guidance:

Not all manufacturers incorporate a preset limit that activates an audible alarm when the quality

of the product water diminishes, but all do offer a process for the user to follow in determining a

suitable limit. The medical director and the chief technician should be able to discuss how the set

point was determined. The response should address the requirement that product water meet

these requirements for chemical contaminants. Different criteria would apply if the RO is

followed by DI polishing.

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The conductivity or TDS of the product water is an important monitoring parameter. There may

be a lower percent rejection in areas where the feed water is fairly pure (e.g., it has a low TDS).

Determining rejection rates may require staff to calculate this from the displayed data. If the RO

does not display rejection rates, expect any staff member assigned responsibility for monitoring

the water treatment system to be able to calculate the percent rejection. Normal ranges should

be known to the operator.

In the absence of an automatic divert to drain valve for the RO, facility staff should demonstrate

knowledge of the requirement to manually stop water flow to the dialysis machines and other

dialysis related equipment (e.g., concentrate mixing stations, reprocessing equipment) should the

water quality alarm sound.