Many people believe that hot water is required to effectively wash your hands; however, the science reveals this to be false. In fact, the International Plumbing Code doesn't require hot water for handwashing stations — it states that “hot or tempered water shall be supplied for bathing and washing purposes” in non-residential occupancies. For new construction buildings, supplying single temperature 75°F water to the handwashing stations reduces the amount of hot water needed and reduces the amount of piping installed in the facility overall. The reduced need for hot water at these stations can enable downsizing of the domestic hot water system, resulting in a smaller DHW load, creating more opportunities for the use of carbon-free heating methods such as solar PV or heat recovery.

Technical Description

Design considerations

Domestic hot water (DHW) systems are designed to have a continuous flow of water in the piping system so that the water does not lose too much heat nor give an opportunity for bacteria growth due to stagnant water. The hot water supply and return piping is typically looped through a facility with short branches for supply and return to each individual fixture (sink, lavatory, shower, etc.), allowing the hot water to keep flowing back to the water heating source via the return line so that the water can be reheated and recirculated again through the supply.

According to the 2018 FGI Guidelines for Design and Construction of Hospitals, “handwashing stations shall be provided in each room where hands-on patient care is provided,” (2.1-2.8.7.1). For areas where multiple patients are being served, at least one handwashing station is required for every four patients, and they must be evenly distributed. It is important to recognize that handwashing sinks serve a separate purpose from scrub sinks and sinks located in patient lavatories and toilets, which have other uses aside from handwashing that may require hot water. Only handwashing sinks are being considered in this scenario.

Domestic hot water systems in hospitals have been identified as breeding grounds for pathogens — including Giardia, Cryptosporidium, and Legionella — posing potential health risks to users. Legionella is naturally present in water systems and usually not a public health problem unless the water is warm enough (above 80°F) to support amplification and maturation of the bacteria. When it comes to the idea of washing your hands with hot water to kill bacteria, the reality is that the water temperature would have to be upwards of 120°F (hotter than a person could stand) in order to have an effect on microbial removal. Additionally, FGI Guidelines lists 105-120°F as the allowable temperatures of hot water for clinical use (Table 2.1-4); thus, the code does not allow hot enough water to avoid the range, in which, Legionella can grow. However, by keeping water temperature below 80°F — outside the range where Legionella thrives — the system behaves much like the cold-water system in that Legionella bacteria remain largely dormant.

Figure 1. Temperature range for Legionella bacterial growth

How does this decarbonize?

By eliminating the need for domestic hot water piping throughout most of the building, there is less heating load on the hot water boilers, burning less natural gas (assuming the boilers are gas fired) and, therefore, reducing Scope 1 emissions. Alternate heating sources for DHW systems such as waste heat from HVAC systems could also be considered to further reduce the heating load needed for showers, sanitizing, and food service. Additional benefits include first cost savings on new construction or major renovation by reducing the amount of hot water piping infrastructure that is needed.

Implementation

Barriers: Codes

Uniform Plumbing Code allows AHJ to dictate appropriate use.

The 2021 International Plumbing Code states: "In nonresidential occupancies, hot water shall be supplied for culinary purposes, cleansing, laundry or building maintenance purposes. In nonresidential occupancies, hot water or tempered water shall be supplied for bathing and washing purposes." Tempered water is defined as "water having a temperature range between 85°F (29°C) and 110°F (43°C).

HCAI requires hot water for "clinical uses" and has a maximum allowable temperature of 120°F for anti-scald purposes.

FGI permits a single temperature pipe system, but FGI is not recognized as a guideline in all states. In CA specifically, FGI Guidelines are not adopted, but proposals for most healthcare facility code amendments to the state building codes are based on language in the Guidelines. Guideline requirements may be applied when state regulations do not cover a particular facility type or space. FGI also references American Society of Sanitary Engineers (ASSE) 1070 Standard, which requires water temperature limiting devices intending to supply tempered water to plumbing fixtures. This standard states that, “the device shall be designed with an adjustable outlet temperature that shall include the range 105°F to 110°F (40.6°C to 43.3°C). The device shall operate with inlet cold water temperatures 39°F to 80°F (3.9°C to 26.7°C) and with inlet hot water temperatures 120°F to 180°F (48.9°C to 82.2°C).”

Barriers: Culture

There is a common misconception that hot water is needed for effective handwashing, which is simply false. In reality, “water would have to be scalding hot before its temperature could improve upon the simple act of scrubbing with soap”.

Financial analysis and business case

Facility managers need to consider the following: current dual-pipe systems with cold and hot water; the amount of fuel, piping, pipe hangers, insulation, mixing valves, maintenance issues; and the energy cost and energy-related carbon emissions.

Based on the above case studies, there is a potential cost savings of $2-4 per square foot for a new facility if a single temperature piping system is used for applicable fixtures. These savings stem mostly from the construction cost of the system. There is less piping, pipe insulation, valves, pipe fittings and accessories, and pipe hangers associated with a single temperature system. The reduced amount of materials needed also results in less labor cost needed to install the system. The range of cost savings is dependent on the location of the project, which the case studies demonstrate well. The California medical office building was more expensive to build and saved more money by implementing a single temperature system than the surgical center and clinic in Pennsylvania.

Additional Resources

Healthcare Facilities Today article from December 2021

Mazzetti blog post, 2021, including link to Academy Journal article

Mazzetti blog post, 2018

CDC guidance for hand hygiene

Mazzetti designed a single temperature water distribution system for a Kaiser medical office building in Berkeley, CA in 2016.

The building is 60,000 square feet and finished construction in May 2020. It was permitted under the 2016 code cycle and approved under city permit review with no issues. The owner did not have a lot of resistance to the idea of single temperature water for handwashing, but they did request further explanation on how the system would avoid impacting pathogen growth and handwashing efficacy. Out of 137 total fixtures in the building, 112 of them are on the single temperature system which delivers water in the 75-80°F range. These included all handwashing sinks, lavatories, and staff toilets. Any sink used for clinical purposes still has a separate 120°F hot water connection. The single temperature system is not recirculating due to temperature differential exceeding 5-7°F (hot water is 120°F; the single temperature water is 75°F). The system works well for this building type due to the warm ceiling space maintaining the water in the proper temperature range, eliminating the need for piping insulation throughout most of the building.

While there is currently no data tracking the energy savings of the single temperature water distribution for this building, cost data is available and relevant! Construction of the system resulted in $250,000 savings, compared to that of a normal HW/CW system, due to the reduced amount of piping, insulation, and mixing valves needed.

Nemours Children’s HEALTH Malvern is a planned 45,000sf Ambulatory Surgical Center and Specialty Care Clinic to open in 2024 as part of the Nemours Children’s Health System. It will be located in Malvern, PA, a northwest suburb of Philadelphia.

The new facility will utilize a single-pipe domestic water system that will supply tempered 75°F water throughout the building to serve handwashing sinks and lavatories. This approach replaces the traditional hot and cold water connections to handwashing stations and eliminates point of use mixing valves at each fixture. Traditional hot water (130°F) will be delivered to limited plumbing fixtures that require local temperature control such as surgical scrub sinks and showers. Out of 137 total fixtures, 96 of the handwashing fixtures will utilize the single-pipe supply system. The single-pipe approach significantly reduces the quantity of domestic water piping, eliminates point of use mixing valves, and eliminates the need for insulation on the tempered water line. In total, the system has an estimated construction cost savings of $99,000 and is expected to significantly reduce operational energy use and maintenance costs.

Despite these financial benefits, the initial decision to use single-pipe in lieu of conventional hot and cold water supply was based on the potential for improved infection control. The tempered water can be maintained at 75°F which is outside of the prime propagation range for Legionella bacteria. In addition, the reduction in mixing valves, which can be a harbinger of bacteria, and the reduced total system volume, which can make flushing the system easier, reduces the risk of Legionella propagation in the system. Designed by the MEP Engineering firm Barton Associates, the tempered water supply system will have an independent hot water heater. Adding recirculation to the tempered water supply system further ensures that any Legionella that is present in the municipal supply system is instantly killed in the 160°F domestic hot water storage tank.