Written and maintained by CASRAI Editorial Board
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This page describes products and general use; it is not medical advice.
Short answer: there is no single rule for autoclave water. Some steam sterilizers require steam-process distilled water, some accept distilled or deionized water, and some laboratory autoclaves say distilled water is unsuitable unless the unit has been adapted. The water your model needs is the one its operator’s manual names. The manufacturer manuals for reservoir-fed units exclude tap water.
Who this is for: clinic staff, lab technicians and buyers who fill, or specify the water supply for, a steam sterilizer and need to know what “autoclave water” means for their unit. After reading, you should be able to find the right water statement in your manual and recognise why two manufacturers can give opposite answers.
What autoclave water has to do
An autoclave turns water into steam, and the water also touches heaters, valves, pipework and level sensors. Dissolved minerals can leave scale on heaters and affect level sensors and valves, according to the laboratory-autoclave maker Priorclave. Some units also use the water’s electrical conductivity to detect whether water is present, so water can be wrong in two directions: too many dissolved solids, or too few. For the general design of the machine, see what an autoclave is; for feedwater as part of a site installation, see autoclave installation requirements.
Distilled, deionized, softened and tap water: what three manuals say
The table compares the water statements in three manufacturer documents. They disagree, which is the main point: “use distilled water” is a model-specific instruction, not a universal one.
| Document (type of unit) | What it says about water | Key figures stated |
|---|---|---|
| SciCan STATIM 2000/5000 G4 operator’s manual (cassette table-top sterilizer for health care) | Use only steam-process distilled water. Deionized, demineralized or specially filtered water should not be used. Never use tap water. | Less than 5 ppm total dissolved solids (conductivity below 10 µS/cm). Other impurities or additives will cause an error reading on the display. |
| SciCan STATCLAVE G4 operator’s manual (table-top steam sterilizer for health care providers) | High quality distilled water is recommended. Deionized, demineralized or specially filtered water can also be used. Never use tap water. | For the external tank with automatic fill: conductivity of 6.4 ppm / 10 µS/cm or less recommended. |
| Priorclave “Autoclave Water Quality and Management” (UK laboratory research-grade autoclaves) | Distilled or ultra-pure water is unsuitable unless the autoclave has been specially adapted. A sodium ion exchange softener is recommended for hard water. | Total hardness as CaCO3 below 50 mg/L; conductivity above 100 µS. |
The two SciCan models come from the same manufacturer yet differ on deionized water: the STATCLAVE manual allows it and the STATIM manual forbids it. Always follow the manual for your specific model, not the one for a sibling product.
Why conductivity limits cut both ways
The STATIM manual sets a ceiling: water above its limit, or containing additives, produces an error. Priorclave describes the opposite problem for its laboratory units. Extremely pure water prematurely corrodes copper pipework and brass valves and fittings, and the heater-protection and water-level controls use the water’s conductivity to detect it. That is why Priorclave recommends softened water that still conducts, rather than distilled water, for those machines. Both statements are true for their own machines, because the machines are designed differently: a cassette unit fed from a reservoir versus a laboratory unit whose controls sense the water’s conductivity.
Check the water-quality statement in your own model’s documentation before choosing a water supply.
Is “autoclave water” different from distilled water?
“Autoclave water” is not a separate product category. It is whatever water the manufacturer specifies for that machine: steam-process distilled for the STATIM, high quality distilled (with deionized acceptable) for the STATCLAVE, softened water within stated hardness and conductivity for the Priorclave units. For how laboratory water grades are defined, see Type 1 laboratory water grades.
Which water for which kind of sterilizer
| Sterilizer type in the source | Source’s water instruction |
|---|---|
| Cassette table-top (STATIM) | Steam-process distilled only; no deionized, demineralized or filtered; no tap. |
| Table-top with reservoirs (STATCLAVE) | Distilled recommended; deionized or demineralized acceptable; no tap. |
| Laboratory research-grade autoclave (Priorclave) | Softened mains water within stated limits; distilled unsuitable unless adapted. |
For how steam-generator and house-steam designs differ in their water supply, see steam-generator vs house-steam autoclaves.
Reservoir fill and chamber water basics
- Fill reservoirs only with the water the manual names. The STATCLAVE quick-start instructs filling both the clean-water and Venturi reservoirs with high quality distilled water.
- Chamber water becomes more concentrated over repeated cycles. Priorclave advises draining, flushing and cleaning the chamber at least monthly, ideally weekly, and draining spillage immediately.
- Softened water raises sodium content over time (Priorclave), which is one reason regular flushing is recommended.
- Where the manual gives a troubleshooting entry for wrong water (the STATIM manual does for water that is not steam-process distilled, or improperly distilled), follow its empty-and-refill instruction.
For routine upkeep see the autoclave preventive maintenance checklist and autoclave troubleshooting.
Common mistakes
- Using tap water in a reservoir-fed unit. Both SciCan manuals say never to.
- Assuming deionized equals distilled. One SciCan model allows it and another forbids it.
- Assuming purer is always better. Priorclave says very pure water can corrode copper and brass and defeat conductivity-based level sensing on its units.
- Applying another manufacturer’s rule to your machine instead of reading your own manual.
FAQ
Can I use tap water in an autoclave?
Not in the reservoir-fed SciCan units: both manuals say never to use tap water. Priorclave’s laboratory units use mains water treated by a softener to stay below 50 mg/L hardness as CaCO3, so untreated hard tap water is not what that manufacturer recommends either.
Can I use deionized water instead of distilled?
It depends on the model. The STATCLAVE manual says deionized or demineralized water can also be used; the STATIM manual says it should not be.
Do I have to use distilled water in every autoclave?
No. Priorclave states distilled water is unsuitable for its laboratory research-grade autoclaves unless specially adapted. Check your model’s manual.
What is the difference between autoclave water and distilled water?
There is no separate “autoclave water” definition; the term means the water your manufacturer specifies for that machine, which may be distilled, deionized or softened.
Sources
- SciCan, STATCLAVE G4 Operator’s Manual, 95-115362 CA EN R5 (checked 2026-10-30): manufacturer manual (PDF).
- SciCan, STATIM 2000/5000 G4 Operator’s Manual, 95-113364 Rev 1.0 (checked 2026-10-30): manufacturer manual (PDF).
- Priorclave Ltd, Autoclave Water Quality and Management, 20 December 2018 (checked 2026-10-30): manufacturer technical note (PDF).
