This is the second in our two-part series of blog posts hoping to clarify (ha!) issues around tap water quality and the impact it may have on sterilization in your facility. In our first post, we focused on the potential long-term effects of using hard water for your steam autoclave.

(SHORT VERSION: Tap water works fine in steam autoclaves, but will drive up your costs and wear down your autoclave over time.) 

But we’re also hearing suggestions that one cannot properly sterilize with tap water. Some claim that it takes highly pure water to achieve full sterility. 

Simply put, this is not the case for typical lab processes: tap water is fine for the vast majority of steam autoclave users in research, education, industrial, or food & beverage situations. 

So Who Should Worry About Using Tap Water in a Steam Autoclave

While tap water is fine for most non-medical autoclave users, it is often not ideal in a medical setting (or some medical research niches). This is the case if:

1. You’re working with extremely dangerous and hearty pathogens in a healthcare setting
2. You need to run back-to-back sterilization cycles 24/7/365, and
3. You’re sterilizing items that are going directly into an injured or immunocompromised person 

Incidentally, if you are sterilizing surgical instruments for use on live subjects or patients, you should not be taking our advice! Listen to folks like the ones here. At Priorclave North America, we specialize in steam autoclaves for education, research, industry, and food & beverage applications. 

“Soft Water” ≠ “Pure Water”

Pathogens are always the primary concern in healthcare settings. As the Association for the Advancement of Medical Instrumentation (AAMI) explains in their current Technical Information Report (TIR34):

“Softened water is water that receives limited treatment (softening) to remove inorganic material from the water. It will not reduce microbial levels, nor will it remove organic material from the water.”

Even softened, tap water will contain bacteria and endotoxins (albeit at low levels, safe for consumption by humans). While bacteria is killed by sterilization, the bacterial bodies and endotoxins aren’t completely destroyed or removed. While this makes no difference in most university labs, it’s a concern with patient care. For example, endotoxins can cause inflammation that slows the healing process or otherwise interferes with treatments.

(In the abstract, endotoxins could affect lab experiments, like certain cell cultures. But we have yet to hear of that in the field.)

In general, facilities that sterilize high-volumes in healthcare settings using FDA-approved autoclaves operate off of a water supply that has been purified or otherwise treated beyond simple softening.  

Hard Water Scale Can Harbor Microbes

The second concern is that untreated hard tap water will tend to leave behind scale deposits that may harbor hearty microbes. 

Scale deposits can form on reusable items (like surgical instruments) or within the autoclave chamber itself. Here, scale is something of a double threat, as it can serve as both a safe-haven for bacteria and spores (creating heat-insulated bunkers that protect them from the sterilizing steam) and provide a food source (some bacteria can use scale mineral deposits as a food source). 

Again, while certainly possible in the lab, we have yet to ever hear of this being an issue in a research, industrial, or education setting. And, at any rate, if you do contend with especially “hard” (i.e., mineral-rich) tap water, a consumer-grade water softener will take care of it.