Javelle water or Javel water, Fr. eau de Javelle, aqueous solution of sodium or potassium hypochlorite. It was originally made near the French town of Javelle (now part of Paris) and was the first chemical bleach, a use first demonstrated by C. L. Berthollet in 1785. It was produced by passing chlorine gas through a water solution of potash (potassium carbonate). After the invention of bleaching powder Javelle water was sometimes produced by reacting the bleaching powder with potash or soda ash (sodium carbonate). Now usually sodium hypochlorite solution, it is used in bleaching and as a disinfectant.