配水系统内的水质恶化。为了防止微生物再生，同时避免客户抱怨味道和气味或消毒副产品浓度过高，水处理的一个重要目标是去除天然有机物:NOM是氯快速衰减的原因，以及消毒副产品形成和细菌再生的来源，通常，水质差。因此，在巴黎郊区要特别小心移除NOM。处理（初始TOC在2至4 mg C/l之间）包括混凝、絮凝、沉淀、砂滤、高级氧化、颗粒活性炭过滤和后处理- 氯化。处理目标是总有机碳低于2 mgC/l，成品水中可生物降解的有机碳水平低于0.3 mgC/l。在这些条件下，0.2 mg/l的游离氯在网络中仍然足够有效，以防止高平板计数和大肠菌群再生问题。由于管道系统的长度和储存设施的数量，重要的是在不增加处理厂消毒剂剂量的情况下补偿消毒剂的衰变。在分配系统的大约57个点引入了氯。这种处理策略产生了令人满意的结果，消费者水龙头处的总三卤甲烷浓度保持在35 ug/l以下。

Water quality deteriorates within distribution systems. To prevent regrowth of microorganisms, and simultaneously avoid customers' complaints about taste and odor or excessive disinfection byproducts concentrations, an important objective in water treatment is the removal of natural organic material: NOM is the cause of rapid chlorine decay, together with the source of disinfection byproducts formation and bacterial regrowth, and generally, a poor water quality. Therefore, particular care is taken in the Suburb of Paris to remove NOM. The treatment (initial TOC between 2 and 4 mg C/l) includes coagulation, flocculation, settling, sand filtration, advanced oxidation, granular activated carbon filtration and post-chlorination. The treatment objectives are less than 2 mgC/l of total organic carbon and a biodegradable organic carbon level inferior to 0.3 mgC/l in the finished water. Under these conditions, 0.2 mg/l of free chlorine is still efficient enough in the network to prevent High Plate Counts, as well as coliform regrowth problems. Due to the length of the pipe systems and the number of storage facilities, it is important to compensate for the disinfectant decay without increasing the disinfectant dose at the treatment plant. Chlorine is introduced at some 57 points in the distribution system. This treatment strategy gives satisfactory results, and the total trihalomethane concentrations remain below 35 ug/l at the consumers' tap.