[The disinfection technology with bleaching powder for drinking water in Shanghai from 1920 to 1983]

Bleaching powder served as the primary disinfectant for drinking water in both urban and rural areas in Shanghai from 1920 to 1983, particularly in rural regions. The liquid chlorine disinfection was introduced by the Yangshupu Water Plant in 1920, marking the inception of chlorination disinfection practice in China. The measures for a drinking water sanitation management framework, taken by the Shanghai health administrative authorities in the late 1920s, laid the foundation for the widespread adoption of bleaching powder. Bleaching powder was extensively applied to public water sources including wells and riverbanks against cholera during the 1930s. In terms of technological practice, bleaching powder was used directly as powder, then gradually improved as liquid, followed by chlorine bleach tablets. After that, two chlorination methods were developed: single-dose chlorination and continuous chlorination in order to solve problems such as poor stability, excessive residue and inaccurate dosing. The driving force for the use of bleaching powder and epidemic prevention was technology dissemination to support public health led by the government. Bleaching powder disinfection represented a pivotal shift from traditional empirical approaches to modern chemical treatment of decentralized drinking water systems in Shanghai, meeting the practical demands for stability, convenience and safety.