将：为尽可能排除无关因素对实验的影响研究区域应作为一个独立的排水片区区域内排水管道雨污分流彻底污水管道内部无淤堵且保持低水位正常运行状态无地下水或湖水入侵至污水管网现象。经现场调查、测绘与检测确认选取中国天津市某区域整个区域占地1538077平方米区域位置分布如图1所示。该区域内共有办公类、住宅类及餐饮类三种建筑类型经统计包含洗漱行为、淋浴行为、舆洗室行为、餐厨行为及餐具清洗行为对研究区域内涉及不

To minimize the influence of irrelevant factors on the experiment, the study area should be an independent drainage area, with complete separation of rainwater and sewage in the drainage pipes within the area, no blockage in the sewage pipes and normal operation with low water level. There should be no groundwater or lake water intrusion into the sewage network. After field investigation, mapping and testing, a certain area in Tianjin, China was selected for the experiment, with a total area of 153,807.7 square meters and distribution of different building types including office buildings, residential buildings and restaurants, involving various water usage behaviors such as washing, showering, toilet flushing, cooking and dishwashing, as shown in Table 1. The impact of different water usage behaviors on the δ34S of tap water and the change pattern of δ34S at the end of the monitoring area were discussed. A monitoring plan was designed, with sampling of sewage generated from different water usage behaviors at different monitoring points during the dominant time periods using an automatic sampler. Tap water samples were collected from the tap using a sampling bucket. Sampling was conducted for three days, resulting in 48 samples, with δ34S as the monitoring indicator. In addition, continuous monitoring of the δ34S in the sewage at the end of the drainage area was conducted for 72 hours to study its variation pattern and corresponding uncertainty differences. The monitoring point was located at the end of the drainage area within the study area (point M), with simultaneous sampling of the sewage generated from different water usage behaviors to ensure the collected sewage was extracted and flowed downstream through point M. The monitoring points for the experiment are shown in Figure 2, with details presented in Tables 2 and 3. The δ34S testing methods used in this study followed relevant national standards. Due to various factors such as testing methods, the absolute abundance of stable isotopes in natural water and many other natural substances cannot be accurately measured. Only the relative difference between the heavy isotope and the light isotope with a relatively high abundance can be measured, expressed as the relative difference between the ratio θ_A and the corresponding ratio of a specific standard reference material θ_R. This difference is known as the δ scale or δ value of the isotope composition, as defined in Equation (1)