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Tap Water and Sterilization (pt. 1): Is Tap Water Bad for Your Steam Autoclave? 

Is Tap Water Bad for Your Steam Autoclave?

We’ve noticed a recent uptick in concerns about water quality and its impact on sterilization and steam autoclave operation. It seems like the biggest source of confusion is a lack of clear differentiation between “medical” sterilization (i.e., the sort that must comply with GMP/GLP) and “research/industrial” sterilization. In general, while tap water may not meet some expectations for steam autoclave sterilization in a medical setting, tap water is fine for the vast majority of steam autoclave users in research, education, industrial, or food & beverage situations.

Over the next two blog posts we’ll clear the waters (ha!) a bit. This week, we’ll discuss the impact water quality has on your steam autoclave itself. Next week, we’ll discuss how water quality can affect your lab’s sterilization process and procedures.   

Why Worry About Tap Water and Steam Autoclaves?

Water is an excellent solvent. That means that any water—even treated city water straight from the tap or a store-bought bottle of water you just opened—is almost never just water. It is full of minerals, calcium carbonate, magnesium, salts, and organic molecules. In tap water, these are kept to perfectly safe levels for human consumption. Such levels will not interfere with most everyday research and industrial uses, either. When potable water has especially high mineral content, we call it “hard water”. It’s still perfectly fine for daily use and consumption, just a little mineral heavy. 

But hard water is hard on anything that generates hot water (e.g., your dishwasher, your coffee maker, your water heater, or your autoclave). That’s because some of the minerals present in drinking water (like calcium carbonate) are less soluble in hot water. As such, they tend to collect in the hottest part of your water system (e.g., the heating element in your steam autoclave’s reservoir). There they form a white deposits (often called “scale” or “limescale”). 

Over time, that deposit keeps getting thicker. Given time, it will form an insulating layer. This slows water heating and interferes with steam generation. Your autoclave will still do its job, just more slowly. That said, feeding a steam autoclave untreated hard tap water over the long term isn’t great. The continued accumulation of limescale will lead to increased maintenance costs, as you have to take time to clean the heating element and interior of the chamber. It will also drive up utility bills, decreased efficiency, and potentially decrease your steam autoclave’s total operating life-span.  

Protecting Your Steam Autoclave from Hard Water

Fortunately, hard tap water is an extremely easy problem to handle in a lab or industrial setting. Your local hardware store has water testing kits, as do most local pet stores. (Fish lovers worry about water hardness, too.) For $10 or less you can check your tap water quality using such a kit. If hardness is an issue, any water softener from the local hardware or appliance store will soften your water and make it suitable for your steam autoclave.

For the majority of lab/education/industrial autoclave users tap water quality is, at worst, a minor annoyance (and easily addressed).