CHLORINE DIOXIDE
An interesting technology - new and as yet lacking support. This is not to say that one should not consider it, but that it is difficult to spend sums on this technology without a reasonable track record and a measure of support based on sound, unbiased, research. A test was conducted at the University Hospital of Wales, Cardiff, UK and they were unable to achieve their focused objective of no Legionella within a hospital H/W system after spending in excess of $35,000 (US). Current technology has Chlorine Dioxide injected as the purchased gas and also generated at the site with a proprietary device. There are no cylinders of gas to be concerned about with site generation.

INSTANTANEOUS HOT WATER HEATERS (IHWH)
These seem to be making a comeback in spite of problems associated with their use in legionella control. They are, however, more energy efficient than standing H/W tanks, but for Legionella control?

When a H/W storage tank is replaced with an IHWH the problem of bacterial amplification is transferred to the circulating loop, where they've always been. In the event of an "outbreak", the units are rarely capable of generating sufficient heat to maintain the loop at 140F+ while flushing each faucet for X minutes as suggested by health authorities. In a recent article the author explained the pros/cons of two systems, the FEEDBACK and the FEED-FORWARD systems.

In the FEEDBACK system, we have a temperature sensor that modulates a valve to allow more or less steam to enter the Heat Exchanger (HX). As demand increases, so does steam feed, thus set temperature is maintained. In the FEEDWARD system, we have essentially the same thing except that some water is maintained at >158F in the HX. However, somewhere in the system we will have that cold, contaminated, city supply entering as makeup, so we've not solved the problem - just postponed it by decreasing total system volume.

COPPER/SILVER IONIZATION
The latest entry into the arena is the Copper/Silver (Cu/Ag) ionization technology. There are currently three firms marketing the devices - two in the UK and one in the USA. The units were originally marketed to replace chlorine use in swimming pools, spas and hot tubs, then they jumped into the potable H/W arena foray for legionella control. The units add, via electrolysis, ions of Cu and Ag from an alloyed electrode such that certain levels of the individual ions are released into the circulating water supply. As H/W flows through the units, the control electronics within the device applies current and causes the dissolution of the electrode such that Cu is maintained at <0.3 ppm and Ag at <0.03 ppm, the target being 0.4 ppm for Cu and 0.04 for Ag. This technique has been reported as efficacious in controlling LB in potable H/W/S. However, a recent 4-year study done at a hospital in Germany suggests that recolonization is possible if Ag levels are allowed to drop below 0.01 ppm (10 ppb), the maximum allowed by law in Germany and France, members of the European Union (EU). A 9-year study conducted at Queen's Medical Center, University Hospital, Nottingham, UK, likewise suggested that the Cu/Ag electronic or alloy technology is not THE answer. Unless the units are properly maintained and water tested using Atomic Absorption (AA) failure, recolonization with LB, is guaranteed.

Rather than go into a lengthy discussion on the units themselves, let us assume the technology is effective and that one would like to apply it, but inexpensively. Instead of an electronic system, one can achieve the same, if not better, control by taking the generic route. Here we have the individual ions being added via chemical feed pumps, a water meter and controller. Each ion is controlled precisely and is not dependent on electrode wear, water quality or other factors affecting the system. The water meter measures the water and actuates a controller that turns on the pumps for every X-gallons of water. Simple, effective and with a focused objective. This technique could also be used by a homeowner.

Is the Silver/Copper technology the answer? Looks like it, right? However, the fly in the ointment is the testing methodology. Other than AA there is no way to accurately determine the levels of silver and copper at levels indicated using available field test kits. That being the case, one would reason that adding individual ions to the water is easier to measure as it exits than paying for the AA analysis on a regular (daily) basis. Let us not forget, at least for health care facilities and hotels/motels desirous of avoiding litigation, that monthly testing of the water supply for LB is a wise course of action.

WHAT ABOUT SILVER IMPREGNATED FILTERS?
No data, no cultures - nothing other than anecdotal testimonials to support claims. The silver has to be in solution at a specified range for any efficacy as proven by data. Also, one cannot exceed governmental levels in the potable supply.

ELECTROLYTIC WATER TREATMENT
The pseudo-scientific verbiage used and outrageous claims make this approach very dangerous where lives are at stake. To the best of my knowledge, there have been no "scientific tests" with cultures and supporting data.