Kettle Descaling Schedule

How often to descale the kettle you boil tea water in, by the hardness of your water. Scale also changes the cup: hard water puts a film on tea and clouds iced tea.

From your water utility’s annual water quality report or a hardness test strip. Grains per gallon × 17.1 = ppm.

BandHardMonthly
Kettle descaling interval by water hardness
WaterHardness (mg/L as CaCO3)DescaleBasis
Soft0–60Every 2–3 monthsFellow: every two to three months with soft water. Kenwood: every three months for very soft water.
Moderately hard61–120Monthly to every 2 monthsNo maker we checked publishes a separate interval. Start monthly and stretch toward two months if the element stays clean.
Hard121–180MonthlyFellow: about once a month in hard-water areas. Kenwood: every month for particularly hard water.
Very hardover 180Monthly, and whenever scale showsThe monthly hard-water interval is the longest gap to allow. Descale early if white scale is visible on the element or base.

Hardness bands are the U.S. Geological Survey’s. 1 mg/L equals 1 ppm in water. For tea, Japan’s Ministry of Agriculture recommends soft water of about 30–80 mg/L; in a 2023 lab study, water at 200 mg/L built a tea film about 35 times stiffer than soft water did.

Citric acid method

  1. Mix 2 spoonfuls of food-grade citric acid into 500 ml of water in the kettle.
  2. Bring it to a boil.
  3. Leave it for at least 30 minutes so the acid can loosen the scale.
  4. Empty it and rinse the inside with fresh water.
  5. Fill with clean water, boil, and pour it away before you brew.

Method from Fellow’s kettle guide. Kenwood suggests 1 part white vinegar to 2 parts water instead, heated to just below the boil, then two rinse boils. If your kettle’s manual names a descaler, use that one.

Signs you are overdue

  • White or chalky crust on the element or base plate.
  • Flakes floating in the water or settling in the cup.
  • A skin on hot tea that cracks when you tilt the cup.
  • The kettle takes noticeably longer to boil the same amount of water.

Film and cloudiness are covered on the tea troubleshooting table.

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Citric acid and water test strips

Sources

Every figure on this page was checked against the linked source on October 1, 2026.

  1. Hardness of Water — U.S. Geological Survey, Water Science School. 0–60 mg/L as CaCO3 soft, 61–120 moderately hard, 121–180 hard, over 180 very hard
  2. Is Descaling Necessary? How Often to Descale a Kettle — Fellow Products. Monthly in hard water, every 2–3 months in soft; 500 ml water + 2 spoonfuls citric acid, boil, sit 30 min
  3. How do I descale my kettle? — Kenwood. Every month for particularly hard water, every three months for very soft water
  4. The proper way to brew Nihoncha (PDF) — Ministry of Agriculture, Forestry and Fisheries of Japan. Sencha 2–3 g per 100 ml, 70 °C (high grade) to 90 °C (middle grade), 90 s; second infusion hotter and about 45 s; soft water of 30–80 mg/L hardness
  5. Tea film formation in artificial tap water — Giacomin et al., Soft Matter, 2023. Calcium, magnesium and bicarbonate drive surface film; citric acid and distilled water prevented it

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