At all stages of the wastewater cycle, technical and social choices are possible, each with cost and financing implications. Communities have, for instance, a choice between the standard of treatment of wastewater (primary, secondary, tertiary, etc). Partial treatment of effluent can be done at a fraction of the cost of full-scale advanced treatment, but with clear benefits, yielding a very favourable benefit-cost result that would be affordable to many poor commu- nities. Many cities have realized the advantages of making progress towards advanced wastewater treatment in several affordable stages, rather than imme- diate adoption of the most sophisticated option (Figure 4).