In India, now there is a differentiation between "gray" water (washer, sinks, showers, etc.) and "black" water (sewage, toilets, etc.) and all newer apartments (which is a common source of living in cities), there are two parallel separate sewage drain systems that lead to separate sewer systems. The "black water goes to a sewage plant for treatment and use elsewhere and the gray water goes to plant with minor treatment and the water is used for irrigation.
The newer developments with single family homes in the scope of and industrial plant and development also have separate systems. The new developments are not wasting money because the large plants are built including housing and some stores and schools (above all) and are built before the plants are completed because the employees are actually involved in the construction and operation.
These are for plants that cover 40 to 100 acres and the first finished products are the walls, streets, stores and schools. - Kind of a conflict with the Indian morality, recognition of education and the respect of different religions.
Unfortunately, the old traditions inherited cannot be applied to the billions of people and housing that have developed the current standards. - It is hard to grasp unless you have been with people that understand the changes and the current educational and economic power of the country.