Why Water Quality is Important When Using a Steam Autoclave

Why Water Quality is Important When Using a Steam Autoclave

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Written by: Scott Mechler

BS Mechanical Engineering, Mechanical Engineer

Water is the lifeblood of a laboratory autoclave. The quality of water you use will drastically affect the lifespan of your autoclave chamber and steam generator, as well as the types of loads that you can sterilize. To understand why, let’s address seven common questions about water quality and how to improve it.

Can I Use Tap Water in My Autoclave?

The answer to this question depends on the quality of your water. There are a number of things that can affect water quality: its hardness, its minerality, whether it contains chlorides and so on. While many laboratories use tap water with their steam autoclaves, this practice can lead to costly downtime and expensive repairs over time, if the water quality is inadequate. Tap water is certainly a practical source for creating steam, but it can also be destructive to your autoclave.

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How Can Tap Water Damage My Autoclave?

Tap water contains a variety of dissolved minerals and salts. Depending on your geographic location and water source (e.g. ground well, lake, river, etc.) the amount of dissolved content can be very high. The more minerals water contains, the “harder” it is. When hard water is boiled into pressurized steam, it leaves behind salt and mineral deposits within the steam generator, pipes and valves. These deposits build up over time like layers of paint. As they build up, they decrease the efficiency and functionality of the steam generator, as well as clogging up pipes and valves.

For an example of how poor water quality can damage your autoclave, take a look at the images below showing the inside of a steam boiler.

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These images show the mineral buildup that can occur in an electric steam generator. The 3rd and 4th images show corroded heating elements sticking out of the boiler flange.  The white “scale” shown here was caused by severe water hardness and silica present in the water and which remains after the water has been continuously boiled.

Scale can wreak havoc on a generator.  Scale is caused from chemicals that are deposited onto a surface and create a hard layer.  Scale can form inside water level sensor tubes, which can cause the sensor elements to malfunction. This can potentially lead the heaters to melt down and fail.

Alternatively, scale could flake off and fall into the shell of the generator, or stay stuck to the surface, where it can form calcium deposits. These calcium deposits are electrically conductive and can create bridges between heaters, which can, again, cause them to short circuit and overheat.

Given the potentially dangerous consequences, it’s imperative that you be mindful of the water quality feeding your autoclave. Consolidated requires that any water that is harder than 5 grains (85 mg/L) should be treated, the potential methods of which we will explore below.

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

Yes, you can start with this report to get a sense of your water quality. However, the water quality requirements for safe drinking water are often different from the water quality requirements of industrial machinery. 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.

Once tested, check to make sure that the water quality falls within Consolidated’s recommended specifications for water quality.  See below.

Types of Water Scale


Can I Feed Deionized Water Into My Autoclave’s Carbon Steel Steam Generator?

No. Deionized and distilled water has been stripped of all minerals, which means it has no electrical conductivity. Consolidated’s standard (carbon steel) steam boilers use conduction-based water level sensors, which means that boilers fed with deionized water can cause intermittent failures. More dangerously, deionized water will leach minerals from any non-stainless metals they are in contact with over time. Over the course of several months, a standard boiler fed with deionized water will develop pits, leaks and other weakening.

For more information about water feed requirements for carbon steel steam generators, refer to the chart below:

Water Feed Requirements, Carbon Steel Steam Generators

Carbon Steel Steam Generators General Vacuum Device & Quench
Characteristic Recommended Condition Maximum Condition Recommended Condition Maximum Condition
Temperature [°F (°C)] As Supplied 140 (60) 40-60 (4-16) 70 (21)
Total Hardness (mg/L) 17 85 10-85 171
Alkalinity (mg/L) 50-180 350 50-180 350
Total Dissolved Solids (mg/L) 50-150 250 50-200 500
pH 7.5-8.5 7.5-9.0 6.8-7.5 6.5-9.0
Total Silica (mg/L) 0.1-1.0 2.5 0.1-1.0 2.5
Resistivity (Ω•cm) 2,000-6,000 26,000 2,000-26,000 500,000


How Can I Purify My Water?

For a carbon steel steam generator, often the easiest and least expensive water treatment solution is to install an RO filter system on your water line and install an automatic generator blow-down feature on your electric steam generator. The RO system would consist of three filters, each of which should be replaced at different intervals:

  1. The prefilter, which should be replaced every two to three months.
  2. The carbon filter, which should be replaced ever four to six months
  3. The RO filter, which should be replaced every year

The RO filter will retain the majority of the contaminants, while the blow-down feature will flush away any minerals that do make it through, thereby greatly extending the life of the heating elements in the steam generator.

In summary, there are actually 4 ways to remove wate impurities, depending on your starting water quality of the feed-water and the material of the boiler.

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 solution for standard carbon steel boilers.
  • Another option for carbon steel boilers is the use of 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 Boilers:

  • 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. Deionized water should only be used to feed  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 virtually all dissolved materials.  Distilled water should only be used to feed  stainless steel boilers.

Learn more about our Autoclave Water Purification Systems, designed to seamlessly integrate with all sterilizers and other laboratory equipment that require purified water.

How Pure Does My Water Need to Be? 

Water between 2,000 to 26,000 ohms*cm (purity achieved with a Type IV RO filter) would be appropriate for the vast majority of research lab sterilizer loads, such as bio-hazardous waste, clothing, cages, glassware, media or general lab equipment.

On the other hand, items that are sensitive to mineral contamination, such as tissue samples or items used in cGMP processes, should only be sterilized by steam generated from water greater than 1 megaohm·cm. Water of this purity is generally only achieved from DI and distilled purification. Keep in mind, when high purity water — greater than 1 megaohm·cm — is used as the source for steam generation, all steam-wetted piping on the autoclave must be constructed from stainless steel, specifically the chamber, jacket, steam generator and process piping.  (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.)

What Should I Do If My Autoclave is Damaged because of Poor Water Quality?

There are a few response tiers based on the severity of the damage. For the first tier — that is, minimal damage — we recommend using Consolidated’s automatic generator blow-down feature to drain out scale, especially for any carbon steam boiler that isn’t fed with purified water.

The second tier of response is to implement a water filtration system, like the Type IV RO filter mentioned above. This water system, which is a step up in complexity from the kind you’d find under your kitchen sink, will remove minerals from your generator and feed it more purified water. This is an acceptable response to all but the most severe cases.

The third — and most severe — response tier is to purchase a new steam boiler or an entirely new autoclave.  This level of damage is most common in areas of very poor water quality where scale likely built up over the course of a few years.
The scale in the steam boiler pictured above qualifies as a severe case and would warrant this response.

For more about water quality and protecting your steam autoclave, visit our Smart Options page.  

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