Due to climate change, water stress and drought related problems are becoming ever more pressing in Belgium and many other countries. There is growing interest in (re)using drainage water from building sites instead of simply discharging it into the sewer system. The potential of the reuse of drainage water is significant, given the yearly volumes (estimated 63 million m3/year in Flanders Region (Belgium) alone). Buildwise conducted a sampling campaign between 2021 and 2024 to gain a better understanding of the quality of this type of water. This showed that the use of drainage water in residential sanitary installations (e.g. for toilets and washing machines) is not recommended without additional treatment.