Considering Tepid Water on Your Project? Here is What You Need to Know

The problem:

We need to provide comfortable temperature water, without the risk of scalding. 

There was a code change some time ago that says we are required to provide "tepid" water (by ANSI definition 60-100 degrees F) to eyewashes and safety showers instead of just whatever comes out of the cold water line. I am sure some poor souls had insult added to injury when freezing water was provided to wash chemicals off their skin after a lab accident. We all know that feeling of jumping in a freezing cold pool or shower - unpleasant and very difficult to stay in long enough to properly rinse chemicals off the skin or out of the eyes. I've had my eye rinsed before, unpleasant even with tepid water. 

Locations where you might want to supply tepid water would be sinks, eyewashes and safety showers. The  traditional way we have provided warm water to locations is to run hot and cold water separately to each location, then mix them with a mixing valve at the point of use. This requires a lot of piping and mixing valves, increasing both first installed and maintenance cost.

It works, it works well, but is expensive. We are seeking a more economical way to achieve this goal. 

The solution...maybe:

So, the tepid water loop is born. You mix cold and hot water at a single point and distribute it as a utility loop around the building solving the problem, right? Not quite. 

Tepid water runs at approximately 75-90 degrees F with the goal being comfortably warm without the risk of scalding. Unfortunately, a lot of bacteria grows in the 75-100 degrees F range putting tepid water in the danger zone for growing uglies like Legionella.  The CDC recommends building water systems run at temperatures higher than 124F and lower than 68F to avoid waterborne microbial contamination. When we run piping systems in this temperature range for the purpose of human contact as in the case of sinks, eyewashes and safety showers, it is considered the same category as drinking water and must be treated as such. 

With any fixture you will have some dead leg or section of piping that is not looped for circulation but instead water sits in the pipe waiting to be used. In the case of a sink, the presumption is that in most cases the sink would be used fairly frequently, and stagnation may not be a concern. This should be considered carefully with the building users and facilities staff during design. If you have sinks that will be used less than a couple of times a week, tepid water may not be for you. 

Eyewashes and safety showers are another matter - they are used only in event of an emergency, so dead legs present a much greater problem. Typically I see facilities staff schedule flushing/ testing of eyewashes and safety showers once per month. Once per month is adequate assuming you have an either cold only feed or a hot/cold mixed at the point of use scenario. With a tepid water loop frequency of flushing needs to be increased to 1x per week. The last thing you want in a safety shower or eyewash is bacteria laden water going into the eyes and mouth putting both your occupants and your company at risk. 

Here is the good news:

If you are located in a moderate climate and your incoming domestic cold water temperature falls within the ANSI Z358.1 temperature range of 60-100 degrees F, you don't need to mix at all to comply with code! 

In healthcare environments, facilities staff may already have a weekly flushing schedule at all fixtures. If this is the case, a tepid water loop with a UV light or other bacterial inhibiting solution may be a viable option. 

The takeaway:

• Consider carefully what your tepid water loop is serving, and how frequently each point of use will be utilized. You can always have the tepid loop serve some things, and mix at less frequently used locations. 
• Check your incoming cold water temperature range to see if it complies with ANSI tepid water definition. You may not need to do anything! 
• Communicate with the facilities staff. Ask what their existing flushing schedule is and discuss the implications of the design and the flushing schedule. 
• Consider all the aspects of this design decision including up front and long term costs or savings.
• Often solutions to one challenge present all new challenges. Make sure to consider all aspects when tempted to jump on a money saving solution, it could cost you far more in the long run.