What does dechlorinating mean?
Dechlorinating is the process of removing chlorine or its compounds from a substance, most commonly from tap water. Municipal supplies are routinely treated with chlorine to kill harmful microorganisms, but residual chlorine can be toxic to fish, amphibians, and beneficial bacteria, and can affect the flavour of drinking water and the growth of some plants. As a result, dechlorinating is a routine step for aquarium owners, pond keepers, brewers, and gardeners, achieved either chemically — using conditioners, tablets, or agents such as sodium thiosulfate — or physically, by letting water stand so free chlorine dissipates, though this passive method does not remove more stable compounds like chloramine. The verb derives from 'chlorine', itself rooted in the Greek 'chloros', meaning pale green. Though technical in register, the word has become familiar through pet care and water-quality discussions.
Removing chlorine or chlorine compounds from water or another substance.
"He was dechlorinating the aquarium water while his daughter watched the filter bubble away."
Typically used transitively; the object is usually water.
The act or process of removing chlorine from a substance.
"Dechlorinating is essential whenever untreated municipal water enters a koi pond."
Functions as a verbal noun naming the process rather than an action in progress.
Aquarists have long known that simply leaving tap water out overnight dechlorinates it naturally — but that trick fails against modern chloramine, which won't evaporate away.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of dechlorinating
The word combines the prefix 'de-', indicating removal or reversal, with 'chlorine' and the verb-forming suffix '-ate'. Chlorine was named in the early 19th century by Humphry Davy, drawing on the Greek 'chloros' (pale green) in reference to the gas's colour. The verb 'dechlorinate' emerged alongside modern water-treatment practice in the 20th century, when concerns about chlorine residues in aquaria and industry created the need for such a term.
Related word forms
How dechlorinating is actually used
A technical term used mainly in water treatment, fishkeeping, gardening, and industrial contexts; it rarely appears in everyday conversation outside these fields. The spelling follows British and American conventions identically except where surrounding text favours '-ize' versus '-ise' forms of related verbs like 'neutralise'.
Easily confused with dechlorinating
Decolorizing means removing colour from a substance, whereas dechlorinating specifically means removing chlorine from it.