Maintaining quality water in a point-of-use (POU) cooler requires regular sanitization of the inside of the cooler in addition to whatever proper filtration or other treatment of the feedwater may be occurring as part of normal cooler operation.

Water reservoirs in coolers are fertile breeding grounds for bacteria and biofilm. Biofilm is a slimy layer that adheres to the surfaces that store water. The film allows for the continued growth of bacteria when the linked network of organisms forms a protective layer which can greatly increase resistance of the organisms in the interior of the layer to chemical disinfectants and sanitizers.

While the United States has no established standards for the frequency and method of sanitizing POU coolers, there are European regulations requiring sanitization of POU coolers every three months.

Beyond filter changes
The bottom line is that proper maintenance and care of POU coolers goes beyond regular filter changes. These coolers also need regular sanitizing to provide consistent, high-quality drinking water.

A variety of methods are available to sanitize POU coolers. These methods can be structured to work manually or automatically, and each method has advantages and disadvantages (see accompanying charts, in sidebar).

While each method, done properly, provides effective sanitization, the methods are not equivalent in terms of cost, resources and effects on drinking water taste.

Common methods
The most common methods of sanitizing a POU cooler involve the use of disinfecting ultraviolet light, ozone or common chemical sanitizers such as chlorine bleach and hydrogen peroxide. The following details these methods:

• Ultraviolet light (UV), at a wavelength of 254 nanometers, inactivates bacteria, viruses and other microorganisms. UV is used for disinfection in POU coolers primarily in three different ways: in-tank, re-circulating and in-line.

  The in-tank and re-circulating methods provide filtered water with constant exposure to the UV light. To be effective, in-line UV should be used after filtration and before water is dispensed, so that water with high clarity (low in solids that could disperse the light) is exposed to the UV light.

• Ozone is an excellent oxidizing agent and bactericide that can be introduced into the reservoir via a built-in ozone device attached to the cooler’s reservoir or a portable ozone generator attached for periodic operation by a trained service technician.
• Chlorine bleach is a strong oxidizing agent and disinfectant formulated to break down organic matter and destroy biological organisms. It is used commonly as a “pour-in” product or as a spray. After contact with a bleach solution, the reservoir should be scrubbed, wiped and flushed.
• Hydrogen peroxide is a strong disinfectant and oxidizing agent used in water-based solutions for disinfecting reservoirs. It is also used commonly as a “pour-in” product or as a spray. Again, after contact, the reservoir should be scrubbed, wiped and flushed.

Consistency is key
Whether you use an automatic or manual method for sanitizing POU coolers, the process must be followed on a consistent basis.

When completed properly, each of the above methods is effective in reducing bacteria and inhibiting the growth of biofilm.

Automatic sanitization methods are more likely to be effective in the long term when they are subject to proper maintenance and care. Manual sanitizing methods will only be effective when completed properly and on a consistent basis.