Verdict: It depends. Distilled water sounds like the obvious fix for scale, but Wolf tells owners of its convection steam oven not to use distilled, demineralized or reverse osmosis water, because its water-level sensor needs minerals to measure accurately; other brands set their own rules.
Where the idea comes from
Steam appliances and hard water don't mix well. Every time water turns to steam, its minerals stay behind as scale, and parts of Los Angeles County have hard water. Distilled water has almost no minerals, so using it seems like a clean way to skip descaling altogether. The same advice is common for irons and humidifiers.
What the evidence says
Wolf's page on convection steam oven water requirements says: "Do not use demineralized, reverse osmosis filtered, or distilled water." It explains that the oven's level sensor is electromagnetic, and "this type of technology requires mineral content in the water for accurate measurement." Tap water, filtered water and softened water can all be used as long as there are minerals in it, and bottled water also works. Wolf supplies a test strip to check hardness before use and says to adjust a water softener as needed to meet the unit's requirements.
Wolf's page on convection steam oven descaling explains the trade-off. Scale is "a natural result of steam creation," and it builds up in the boiler and water lines. The oven typically needs descaling every 6 to 18 months, depending on use and water hardness, and the display shows "Boiler scaled up—please descale!" when it's due. Wolf currently suggests Durgol as the only descaling solution and says vinegar should not be used. It also warns that skipping proper descaling can cause damage.
So the tip is wrong for this oven: the minerals that cause scale are the same ones the sensor relies on.
What to do instead
- Check your steam oven's manual for its water requirements before changing anything.
- For a Wolf convection steam oven, use tap, filtered, softened or bottled water, never distilled or RO.
- Test your water with the strip supplied and set the oven's hardness if it asks.
- Descale when the message appears, with the product the manufacturer names.
- Empty and dry the water reservoir if the manual says to after use.
Exceptions worth knowing
- •Other brands differ. Some steam ovens, countertop steam appliances and irons have different instructions. The manual for your model is the only reliable guide.
- •An RO system on the kitchen tap can affect what you're pouring in. Fill the reservoir from a tap that isn't routed through the RO unit if the manual requires minerals.
- •Very hard water means more frequent descaling, not distilled water, under Wolf's guidance.
- •A fridge filter won't change this. See whether refrigerator water filters soften hard water.
Sources
- •Wolf: Convection Steam Oven Water Requirements (no distilled, demineralized or RO water; sensor needs minerals; tap, filtered, softened and bottled OK)
- •Wolf: Convection Steam Oven Descaling (every 6 to 18 months; Durgol; no vinegar)
The short version: For a Wolf steam oven, use mineral-containing water and descale on schedule; for any other model, follow its manual.
Water or descaling errors that won't clear on a steam oven are worth a technician's look. TrueFix Los Angeles repairs Wolf ovens and other high-end brands; call (213) 787-3989.