Why can't I use tap water in my steam sterilizer?

Water is the lifeblood of a healthcare sterilizer or a laboratory sterilizer. The water quality you use will drastically affect the lifespan of your sterilizer’s chamber, steam generator, and the types of loads you sterilize.

You may be wondering…

Why can’t I use tap water in my steam sterilizer?

The answer to this question depends on the quality of your water. Several things can affect water quality: hardness, minerals, chlorides, etc.

While many laboratories use tap water, the continuous use will eventually lead to significant sterilizer downtime and expensive repairs – especially if your tap water quality is bad. Tap water is a source for creating steam. However, eventually, poor tap water will damage your sterilizer.

Does tap water damage my autoclave?

Tap water contains a variety of dissolved minerals and salts. The dissolved content can vary greatly depending on your geographic location and water source (e.g., ground well, lake, river, etc.).

The more minerals the water contains, the “harder” it is. While hard water is boiling into pressurized steam, water will leave salt and mineral deposits inside the steam generator, pipes, and valves. 

The deposits build up over time, causing the steam generator to degrate, and the pipes and valves to clog.

Scale is your enemy

Did you know that scale is what wreaks havoc on a generator? Scale is chemicals that deposit onto the sterilizer’s chamber surface, creating a hard layer of scale. 

Unfortunately, the scale starts forming inside the water-level sensor tubes, causing the sensor elements to malfunction. Then, eventually, the sterilizer’s heaters will melt down and eventually fail.

Furthermore, over time, the scale flakes off and falls into the generator’s shell or stays stuck to the surface, forming calcium deposits. These electrically conductive calcium deposits create electrical bridges between the heaters, causing them to short-circuit and overheat.

IMPORTANT If water quality is harder than 5 grains (85 mg/L), you should consider treating your water. What is your water quality? Click here to find out.

Can I Use a Municipal Water Quality Report to Gauge Tap Water Quality?

Yes, you can start with this report to understand your water quality.

However, the water quality requirements for safe drinking water differ from those of industrial machinery (like a steam autoclave).

If your municipal water quality report does not indicate the hardness of your tap water, we recommend that you perform an independent water quality test.

Ideally, whether you have the municipal water quality report or now, it is ideal to test the water right before it enters the steam boiler, as building pipes can contribute to water hardness.

Can I use deionized water in my sterilizer’s carbon steel steam generator?


Deionized and distilled water has been stripped of all its minerals. Meaning the water has no electrical conductivity. PRIMUS’s standard (carbon steel) steam boilers use conduction-based water level sensors, which means that boilers fed with deionized water can cause intermittent failures.

Plus, deionized water will suck the minerals off non-stainless metals, and over several months, a standard boiler fed with deionized water will develop pits, leaks, and other weakening.

Water Feed Requirements, Carbon Steel Steam Generators

Carbon Steel Steam GeneratorsGeneral Vacuum Device & Quench
CharacteristicRecommended ConditionMaximum ConditionRecommended ConditionMaximum Condition
Temperature [°F (°C)]As Supplied140 (60)40-60 (4-16)70 (21)
Total Hardness (mg/L)178510-85171
Alkalinity (mg/L)50-18035050-180350
Total Dissolved Solids (mg/L)50-15025050-200500
Total Silica (mg/L)0.1-
Resistivity (Ω•cm)2,000-6,00026,0002,000-26,000500,000

How do I purify the water in my sterilizer?

A simple and affordable water treatment solution for a carbon steel steam generator is to install a reverse osmosis filter system on your water line. The reverse osmosis system consists of a filter that should be replaced yearly.
Additionally, the reverse osmosis filter retains the contaminants, while the blow-down feature will flush away any minerals that make it through the steam sterilization. This reverse osmosis system will significantly extend the life of the sterilizer’s heating elements in the steam generator.

The 4 ways to remove water impurities in your sterilizer’s water source

PRIMUS PRI-pure reverse osmosis system designed to be integrated into a PRIMUS steam sterilizer by spire integrated solutions

Learn more about PRIMUS sterilizer’s PRI-PURE reverse osmosis system – it’s been designed to easily install in the field.

Carbon Boilers

  • Reverse Osmosis (RO) – RO systems filter water by forcing it through a thin permeable membrane that removes most solid contaminants and dissolved minerals but does not remove biological particles, such as bacteria or viruses. An RO system is the #1 recommended standard carbon steel boilers solution.
  •  Another option for carbon steel boilers is using a water softener system. These systems are a chemical treatment that reduces hardness but can leave other impurities dissolved in the water, so is only applicable to customers who meet all water quality requirements except for hardness.

Stainless Steel Boiler 

  • Deionization (DI) – DI systems remove the ions from the water and produce a very high purity level. It does not affect uncharged molecules, viruses, or bacteria. Use deionized water inside stainless steel boilers.
  • Distillation – Distillation removes virtually all impurities from water by boiling it and then condensing the steam into a clean container. This process removes almost all dissolved materials. Use distilled water should only be used to feed stainless steel boilers.

Do I need to use pure water in my steam sterilizer?

Water between 2,000 to 26,000 ohms*cm (purity achieved with a Type IV RO filter) is acceptable for most research laboratory sterilizer loads, such as bio-hazardous waste, clothing, cages, glassware, media, or general lab equipment.

On the other hand, items sensitive to mineral contamination, such as tissue samples or items used in cGMP processes, should be sterilized by steam generated from water more than one megaohm. Steam-wetted piping must be stainless steel if your water purity is greater than one megaohm.

Look what happens to your sterilizer when you use water that is not pure

What happens when you use tap water in an autoclave.  PRIMUS sterilizer by spire integrated solutions.
What happens when you use tap water in an autoclave.  PRIMUS sterilizer by spire integrated solutions.
What happens when you use tap water in an autoclave.  PRIMUS sterilizer by spire integrated solutions.
What happens when you use tap water in an autoclave?  PRIMUS sterilizer by spire integrated solutions.

DID YOU KNOW?  Shine matters!

PRIMUS sterilizer Reverse Osmosis (RO) – RO systems filter water by forcing it through a thin permeable membrane that removes most solid contaminants and dissolved minerals but does not remove biological particles, such as bacteria or viruses. An RO system is the #1 recommended solution for standard carbon steel boilers.

Did you know that the sterilizer chamber surface finish of your steam sterilizer determines its corrosion resistance and how easy it will be to thoroughly clean the autoclave?
It’s true! Have you ever wondered why an autoclave chamber needs to be highly polished?  
Because shine matters, PRIMUS by Spire Integrated Solutions is the only healthcare and life science steam sterilizer manufacturer that offers PRI-Mirror highly polished chambers.
The brilliant PRI-Mirror chamber finish found in all PRIMUS models sets the highest standard for surface finish, achieving a 10 Ra (0.026 microns) measurement.

A highly polished chamber surface keeps your sterilizer “sterilizing” at peak performance. Shine does matter!

DID YOU KNOW? High-purity water lacks ions or dissolved minerals and will try to leach impurities from everything it touches, including carbon steel and copper, and will cause continuous weakening and premature failure of plumbing components manufactured from these materials.

I think my boiler is damaged due to poor water.  What do I do?

First, if your damage is minimal, PRIMUS recommends draining out the scale, especially for any carbon steam boiler not fed with purified water.

Second, implement a water filtration system, like the PRIMUS PRI-Pure reverse osmosis system. This reverse osmosis system will remove minerals from your generator and feed it purified water.  This is how you install the PRI-Pure reverse osmosis system.

Thirdly, you may need to purchase a new steam boiler, healthcare sterilizer, or life science PRIMUS sterilizer.  This level of damage is most common in areas of poor water quality – where scale has built up over time.

More information

Have a question or having difficulties? Talk to Dave Schall, our PRIMUS sterilizer expert who is here to assist you anytime at 877.679.7800 extension 1212 or email at dschall@spire-is.com.

Visit us at spire-is.com

Back to Blog