Also called: Autoclave water, Distilled water, Feed water quality
Autoclave Water: Choosing and Checking Feed Water
Feed water is the cheapest thing in the autoclave room and the most common cause of faults. What “good enough” water means, and how to keep it that way.
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Why tap water ruins an autoclave
Scale
Calcium and magnesium come out of solution as steam forms, building scale on heating elements, in steam generators and in valves until they stick or leak.
Corrosion
Chlorides from treated water attack stainless steel, causing pitting on instruments and inside the chamber.
Stains and residue
Silicates, iron and dissolved solids leave white, brown or blue-black marks on instruments and deposits on packs.
Faults and wet packs
Blocked valves and sensors cause aborted cycles, poor vacuum and wet loads — and many makers will not honour a warranty claim caused by poor water.
How pure is pure enough
Water purity is measured as conductivity in microsiemens per centimetre (µS/cm): the fewer dissolved ions, the lower the number. Feed water for small sterilisers is commonly specified at around 15 µS/cm or lower, with very low hardness, chloride and silicate, and large hospital sterilisers usually need purer water still. Treated tap water is many times higher than that. Your manufacturer’s figure is the one that counts — check the manual.
- A pocket conductivity (EC) meter is inexpensive and the simplest check on every new batch of water.
- TDS meters read in ppm rather than µS/cm; on common settings the ppm figure is roughly half the conductivity, so convert before comparing.
- Test fresh water, and test again if packs start spotting or the autoclave flags water quality.
Distilled, deionised or RO?
| Water source | How it is made | Strengths | Watch out for |
|---|---|---|---|
| Distilled | Water is boiled and the steam condensed | Consistently low minerals; no cartridges | A benchtop distiller takes several hours for a few litres; containers must stay clean |
| Deionised (demineralised) | Ion-exchange resin removes dissolved ions | Very low conductivity when the resin is fresh | Purity drops suddenly as the resin is used up; does not remove bacteria |
| Reverse osmosis (RO) | Water is forced through a membrane | Removes most dissolved solids; can be plumbed in | RO alone may not reach the limit; often paired with a deionising polisher; tanks can grow biofilm |
| Bottled drinking or mineral water | Packaged for drinking | — | Contains minerals by design — not suitable |
Buying, storing and handling water
- Buy distilled or deionised water from a reliable source. Water sold for car batteries is not made for medical equipment and its quality varies, so test it.
- Store it in closed, clean containers out of sunlight, and label the opening date.
- Never top up an old reservoir or container with new water — empty, rinse and refill.
- Use a clean jug or funnel kept only for autoclave water.
- If you use a plumbed-in RO or deionising unit, replace filters, membranes and resin cartridges on schedule, and watch its outlet conductivity reading.
Reservoirs, sensors and water systems
Single-use water
Some autoclaves use fresh water for every cycle and send used water to a separate waste tank. Purity stays consistent, but the waste tank must be emptied and cleaned.
Recirculated water
Others reuse the reservoir water for several cycles. Drain, rinse and refill it as often as the manual says, because impurities build up with each cycle.
Water-quality sensor
Many units measure conductivity and stop or warn when it is too high. Never bypass the warning — change the water and find the cause.
Read next Full autoclave maintenance checklist
Related guides
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Frequently asked questions
Can I use tap water in an autoclave?
Is RO water good enough for an autoclave?
What conductivity should autoclave water have?
Can distilled water for car batteries be used?
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