Manufacturers are actively researching new on demand hot water heater designs, products, and technologies. However, since these are not particularly high volume sales items, research and development is often slow.
Few studies have evaluated the water saving potential of these devices. A 2000 study in Westminster, Colorado evaluated on demand hot water systems in six homes and in a group of control houses (Mayer and DeOreo, 2000). This study found evidence of reduced shower usage in the six homes with the on demand systems. However, these six homes used more water for baths than did the control group. The combined shower and bath usage was identical between the two study groups. The study concluded that there was “no statistically verfiable overall savings” associated with the on demand hot water systems, either because of the effectiveness of the systems or because of the small sample size.
A recent unpublished study by the Santa Clara Valley Water District in San Jose, California evaluated on demand hot water systems in about ten single-family houses (de la Piedra, 2001). This study found limited water savings in the study homes. These savings were substantially less than the manufacturer had claimed.
If these devices are to be included as part of comprehensive water conservation programs they must be shown, through independent evaluation, to save water. At this point water saving potential of on demand hot water systems is uncertain.