CMS SOM App. H, Tag V208

5.3 Water storage and distribution

5.3.1 General: Design

A water storage and distribution system should be designed specifically to facilitate

bacterial control, including measures to prevent bacterial colonization and to allow for easy

and frequent disinfection.

Interpretive Guidance § 494.40(a)

ANSI/AAMI RD52:2004

5.3 Water storage and distribution

5.3.1 General

The function of the water storage and distribution system is to distribute product water from the

purification cascade to its points of use, including individual hemodialysis machines,

hemodialyzer reprocessing equipment, and concentrate preparation systems. A water storage

and distribution system typically contains a large volume of water exposed to a large surface

area of piping and storage tank walls. Because chlorine and chloramines are removed in the

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purification process, the water does not contain a bacteriostatic agent. This combination of

circumstances predisposes wetted surfaces to bacterial proliferation and biofilm formation.

5.3.3 Water distribution systems

Two types of water distribution systems are used: direct feed systems and indirect feed systems.

In a direct feed system, water flows directly from the last stage of the purification cascade to the

points of use. In an indirect feed system, water flows from the end of the purification cascade to a

storage tank. From there, it is distributed to the points of use. In general, direct feed systems

offer the least favorable environment for bacterial proliferation. However, with a direct feed

system the purification cascade must be sized to provide sufficient water to meet the peak

demand, and the system must have sufficient pressure at the end of the purification cascade to

distribute the water to the points of use. Those two requirements often preclude the use of a

direct feed system.

AAMI Rationale for the Development and Provision of This Recommended Practice

A.5.3 Water storage and distribution

Direct feed water distribution systems typically return unused water to the feed side of the

reverse osmosis unit. If the pressure at the end of the distribution loop decreases to a value

below the water pressure at the inlet to the reverse osmosis pressurizing pump, retrograde flow

of non-purified water into the distribution loop can occur. To minimize this risk, the AAMI RDD

Committee recommends that dual check valves be used to prevent retrograde flow and that the

pressure at the end of the distribution loop be monitored.