This set of drawings is good enough for you to go directly to the design institute after work. It contains the "flow chart" you want. Design students can't just look at the flow chart, it's rough. You should find a set of good drawings from some good big design institutes to learn, and make rapid progress.
The sewage treatment flow chart you asked for. Many of my drawings here are construction drawings of large sewage treatment plants. Just ask me for it in the future.
Besides, there are many drawings of Netease Water Supply and Drainage and Water World, which you can easily download and study.