Collecting rainwater for use in toilets is currently uncommon in Sweden. Technology for treatingrainwater and using it for toilet flushing is only found in three buildings in Sweden today. Twoof these buildings are Celsiushuset in Uppsala and Sergelhusen in Stockholm. The buildings thatutilize this technology are relatively newly constructed, and there has been no investigation intohow the systems have performed in terms of operation, efficiency, or user experience. Thesystems in Celsiushuset and Sergelhusen have only been in use for a little over two years andhave not been evaluated during this time. The actual efficiency of the systems is thereforeunknown, and investigations need to be conducted to analyze their efficiency, user experience,and any issues related to system management. This thesis has been conducted in collaboration with Structor Mark Uppsala, which has designedthe external part of the system in the aforementioned buildings. The thesis work has been carriedout using surveys, observations, document analysis, and interviews. The study reveals that thereis some discoloration of the toilet water, which has had an impact on the water and sanitationcomponents. The investigation also shows that most users do not have a problem with moderatediscoloration of the toilet water as long as they are aware of the cause of the discoloration. The amount of rainwater used compared to drinking water in the Celsiushuset system wascalculated to be 12.7 percent since the building's commissioning, but the theoretical efficiency isaround 50 percent. For Sergelhusen, it has not been possible to calculate the actual efficiency, butthe theoretical efficiency is approximately 40 percent. Celsiushuset has had issues with theoperation of the system's control, resulting in the dry-run protection of the pump tripping whenwater should be pumped into the building from the reservoir. Sergelhusen has needed to modifythe system due to excessively high levels of discoloration in the water and has installed additionaltreatment steps, which have led to reduced discoloration. The study shows that discoloration in the toilet water does not have a negative impact on the user'sexperience. However, it is important to consider the choice of materials for the roof and water andsanitation components that are affected by the use of rainwater. Furthermore, the design of the roofis crucial regarding the use of green roofs, which has a significant impact on the quality ofrainwater and requires additional treatment steps in the system.