In today's world, where water scarcity is one of the most important issues, the reuse of wastewater is seen as the key to solve the problem. The most proper solution is to collect greywater, which has relatively low pollution, separately before entering the sewer system. The greywater collected from kitchens and bathrooms can be served to the individual users and it can be used as flush water after being treated in a common treatment plant. In the model building studied in this paper, the toilets of the apartments on the same floor were located close to the vertical shift, so that the length of the pipes for additional infrastructure required for the collection of wastewater was minimal. The reuse of the treated water was also possible when greywater lines were added to the existing lines. In the study, capital and operation and maintenance costs of these infrastructures and treatment plant to be constructed are presented. The treatment alternatives that had been comparatively evaluated were rotating biodisc, membrane bioreactor, and nanofiltration systems. To conclude, it was found feasible to use greywater especially in multi-block and/or high-rise buildings with 160 or more apartments, at the same time it is concluded that the treatment technology with the highest benefit-cost ratio is the nanofiltration system.