The Water Quality Association (WQA) is an international trade organization representing members of all facets of the water treatment industry. One of their focus areas is water softening and its beneficial effects on equipment, clothing, and public perception of water quality. However, as with many other industries, the members recognize that consumers are increasingly focused not just on the direct benefits associated with a product, softened water in this case, but are concerned with the effect of a product on the environment.

The Water Quality Research Foundation (WQRF) initiated a study which was conducted by the Battelle Institute to test devices fed with softened and unsoftened water under controlled laboratory conditions designed to accelerate the waterside scaling in Tankless Gas Water Heaters and quantify the performance efficiency.

This portion of the study was conducted to investigate the interaction of water hardness levels on the performance of tankless water heaters. They also wanted to quantify the amount of scale formation within the hot water heater due to hard water as well as forming an opinion about the life span of the hot water heater as it is affected by hard water deposits.

Battelle set up and tested 10 Tankless Gas Water Heaters with 199,000 Btu/h burners using an accelerated scaling methodology developed at Battelle.
Five were tested without any preconditioning of the water supply, and the other five were tested using a water softener to remove hardness from the water supply. Five units were chosen in order to be able to calculate 95 percent confidence intervals for the results.

At the start of the test, and at approximately one week intervals, the thermal efficiency of each water heater was measured to determine the change in efficiency as waterside scale built up in each water heater. Each water heater
was instrumented to measure the inlet and outlet water temperature at 15-second intervals, the amount of hot water generated, and the amount of gas energy used to produce the hot water. These data were used to calculate the average thermal efficiency of the water heater.
The economic savings of softened water with tankless water heaters can lead to recovery of the cost of a water softener and operating supplies in a period as short as a year, if the incoming water issufficiently hard.

In summary, with softened water tankless gas water heaters operated on softened water maintained the original factory efficiency rating over a 15-year lifetime, while with hard water they failed to function because of scale plugging in the downstream plumbing after only 1.6 years of equivalent hot water use on 26 gpg hard water.
Tankless water heaters fed with softened water save 40% of costs compared to operating on 20 gpg of hard water and saves 57% compared to operation on 30gpg of hard water.