There is one provision in both the Uniform Plumbing Code (UPC) and International Plumbing Code (IPC) that endangers public health and bloats construction budgets: the requirement to provide hot water at all public lavatories. 

The idea that you should “always wash your hands with warm soapy water” has been repeated for decades by federal agencies, health department restaurant placards, and hospital regulations, and is embedded in the model plumbing codes. We would generally have no reason to question such a universal truism, especially one that falls into the sacred category of “things that Mom told us.” 

However, research demonstrates not only that handwashing hygiene is equally effective using cold water or hot, but also that the distribution system for hot water provides an environment that supports the growth of bacteria. The concurrent increases in construction cost, carbon emissions and operating costs from hot water handwashing may pale in importance when compared with the public health hazards, but are themselves significant.

Perhaps without realizing it, you, and millions like you, have already vetted the concept of room-temperature handwashing water many times. The water in the uninsulated section of piping between the circulating hot water and the lavatory rapidly cools towards room temperature, while most users only run the water for 4 – 6 seconds, not nearly enough to draw hot water all the way from the circulating loop to the tap. It may be that few users of public lavatories would even notice this change.

It’s important to point out that there is no need to prohibit hot-water handwashing; individual developers and institutions should be able to decide for themselves whether providing hot water is worth any additional risk and expense. Facility directors of buildings that primarily serve healthy adults may decide that the risks of maintaining the status quo are acceptably small, while the directors of other facility types may opt for room-temperature handwashing. Allowing the responsible party to make an informed choice is what’s urgently needed.

Hand hygiene

Bacteria and other microorganisms primarily spread among building occupants by hand contact with surfaces, which is why healthcare facilities have lavatories, sanitizer dispensers, and surgical sinks everywhere one looks. Although in recent years many individuals have become hyper-vigilant about touching restroom door handles, all the building’s other door handles are equally contaminated, not to mention the elevator buttons, handrails, and touchscreens. Periodic handwashing does dramatically reduce the bacteria count on your hands, at least until the next time you touch something, but the temperature of that water has no impact at all. (What is important for hygiene is to use soap, and to continue scrubbing your hands for 15 - 20 seconds. Only a fraction of hand-washers has been observed to stick with it for the full 20 seconds, long enough to sing through the “Happy Birthday” song twice.)

Few people appeared to have been paying much attention to this issue until a new code provision was inserted in the 2015 International Energy Conservation Code (IECC), severely limiting the volume of water that can be held in the pipe between a public lavatory and the circulating hot water loop. The intention to get hot water to the users more quickly, so that the reduced flow time would reduce water heating energy use. As the new code was adopted around the country however, this provision was found to be more disruptive and expensive than expected, and has been provoking considerable resistance among contractors. While individual mini-tank or demand water heaters at each cluster of lavatories could also be used to comply, those solutions would involve considerable cost.

Searching for economical ways to comply with this code provision, designers began questioning whether we really need to provide hot water in the first place. The code mandates hot water at lavatories because it’s been widely believed to be important for hygiene. As noted above however, each researcher studying the influence of water temperature on handwashing has arrived at the same conclusion; washing one’s hands in cold or room temperature water removes bacteria just as effectively as washing them in warm or hot water – the water temperature itself is irrelevant. In fact, use of higher-temperature water increases skin irritation, providing a more vulnerable substrate for formation of bacterial colonies, and potentially causing people such as nurses who should wash their hands often to reduce their handwashing frequency and intensity.

“Nosocomial infections” are infections acquired while in a hospital, and they’re a serious source of liability and hazard for these facilities. (“Nosocomial” could translate from Latin as “Please call my lawyer.”) 

Deaths and hospitalizations from nosocomial infections in hospitals are orders of magnitude more common than those from fire, even though fire safety is rigorously enforced in hospital design. Meanwhile, Legionella and other organisms thrive in the pipes and mixing valves that supply that warm water for the very handwashing that’s intended to prevent disease transmission in the first place. The optimal temperature range for Legionella growth extends 20°F above and below our human body temperature of 98.6°F – clearly not a coincidence – so not only is the provision of hot water unnecessary for personal hygiene, a delivery temperature of 110°F is just right for the growth of microorganisms in plumbing systems. Those who simply rinse their hands under warm tap water without using soap could actually end up increasing the bacteria count on their hands.

Energy waste and operational expenses

The public health hazard created by the code requirement for hot water at lavatories should be sufficient reason to abandon that rule. However, utility bills and carbon pollution considerations provide another strong argument. The heating, reheating and pumping of hot water to the lavatories throughout a building constitutes a modest portion of total building energy use, but the fact that this is often wasted energy, doing more harm than good, makes it a perfect candidate to be an energy efficiency measure. 

However, the current plumbing codes prohibit this. As lavatories are typically the most numerous fixtures on a building’s hot water system, heating and pumping energy use will drop significantly when they’re removed. The combined expenses of utility bills, annual maintenance, periodic repairs, leakage risks, and eventual equipment replacement adds up, especially where this is an unnecessary system in the first place.

Construction cost

A complex system is required to properly heat and circulate water to all the lavatories in a hospital, high school, or office tower: boiler, pumps, piping, insulation, mixing valves, controls, and more. All these components consume space – space in mechanical rooms, ceiling cavities and plumbing chases, as well as service access. If the lavatories were to provide room-temperature water instead, the use of distributed mini-water heaters at kitchens and showers might be a sensible option for serving the modest number of remaining fixtures, so that the entire central system could then be eliminated. If on the other hand a client still prefers to install a circulating hot water system, the length and size of insulated piping required for the building would be reduced, as would the boiler and pump sizes. 

System selection

The best system choice for providing “room-temperature” water might depend on your location. In the American South and other locations where year-round water utility supply temperatures are already within the range of typical room temperatures, water can flow directly to the lavatories. 

In northern climates where incoming water temperatures are too cold for comfortable handwashing, especially in winter, one easy option would be to allow the water to reach room temperature in a tempering tank or oversized pipe. However, the best strategy for these climates might be to incorporate a drain water heat recovery system. Most readers will be familiar with this technology – typically a copper supply pipe wrapped in a tight upward spiral around a section of vertical waste pipe, with the inner face of the copper pipe flattened to maximize contact area. 

Liquids tend to adhere to the walls of vertical pipes while falling, so that enough of the heat transfers through the waste pipe to the incoming supply pipe that the “cold” water will reach room temperature without mechanical heating. This provides a simple, maintenance-free pre-heating system with no moving parts, resulting in significant cost savings. A side benefit of using drain water heat recovery is that the subsequent temperature lift for shower and kitchen water heating would be reduced, speeding up recovery times.

Optimal water temperature

For room-temperature lavatories, water should be delivered at temperatures low enough to prevent bacterial growth, while still warm enough to encourage thorough hand washing. Fortunately, the typical room temperature range of 68° to 75°F aligns nicely with the optimal handwashing water temperature range of 65° to 80°F.

80°F is the maximum safe temperature to prevent Legionella growth, while 65°F is a good minimum temperature range for handwashing comfort. Much below that temperature, tap water feels uncomfortably cold to users, which could discourage adequate handwashing. (For a related reference point, note that the minimum allowable water delivery temperature for laboratory emergency showers is 60°F.)  

68°F is the minimum space heating capability required by the building code, while 75°F is the minimum cooling setpoint permitted for load calculations in the energy code, bracketing the “typical” indoor temperatures. 

There are certainly situations for which warm water is still important for handwashing, specifically where the occupants’ hands are likely to be greasy or heavily soiled, such as at repair garages, greenhouses, or art classrooms. Private lavatories in dwelling and sleeping units should also provide warm water, since they’re used for additional grooming purposes. Beyond these, there are bound to be many other situations where warm water for handwashing is desirable.

Optional, not mandatory

For the above reasons, plumbing code change proposals submitted by Seattle to ICC and IAPMO in 2018 would not prohibit hot water for handwashing, but rather make it optional. Developers and facility managers would then be empowered to make their own decisions about whether hot water at lavatories is worth any additional cost, space, energy use, or health risks. 

At the very least, this proposed change will allow that choice to be made, and give local health departments a legal basis on which to permit that choice. For the many cities and states with carbon reduction and energy efficiency goals, an option to dispense with hot water for handwashing would allow those jurisdictions to incentivize the choice to provide room temperature handwashing water.

Proposed code change language

Based on feedback received regarding the original code change proposals, the simplest formulation appears to be best. The following exception would be inserted at Sections 419.5 and 607.1 of the IPC, or Section 601 of the UPC.

Exception: Lavatories and other handwashing fixtures not serving dwelling or sleeping units are not required to provide hot water or tempered water.

The path forward

Any new code provision generally requires a cost/benefit analysis, to balance the increased construction costs of the proposal against future utility savings or public health protection. In this case however, all the costs and the benefits fall on the positive side of the ledger, seemingly making this an obvious choice for approval. Public health benefits with lower construction and operating costs – a slam-dunk! However, the proposal was swiftly and unanimously disapproved by both the ICC and IAPMO plumbing code committees. 

A friendly engineer took this author aside after one of these debacles and said, “You know, you’re asking a panel of plumbing professionals to approve something that’ll cut into their business. The fact that it permits a smaller plumbing system makes it an uphill battle.” 

The IAPMO proposal is still on the table, through the public comment process (as Item 55), and beyond that are the individual state code processes. To succeed, either of these will need support from concerned design, construction and public health professionals. Change is always a challenging task, but the public health protection provided in this change makes it well worth the effort.

Duane Jonlin, FAIA, is the Energy Code and Energy Conservation Advisor for the City of Seattle Department of Construction and Inspections. He can be reached at Duane.Jonlin@seattle.gov.