Water is an essential natural resource and is even known to be the cause of many wars of history. While people depend on it to survive, they also use it for everyday activities and several other purposes. As for plants, water is an essential factor, one they need for growth. Although irrigation is really important for certain agricultural plants, many criticise its water consumption especially on scientific platforms and media. This naturally pushes the world to find alternative ways to decrease the water consumption where possible. Greywater (GW) use is one of these alternative ways. This study aims to focus on two different but ecologically useful recent phenomena; GW use and green roofs. GW use makes it possible to decrease water consumption by replacing irrigation water, while green roofs (GRs) are known to increase biodiversity in urban areas and to decrease heat island effect and as a result reduce the costs of air conditioning. Since the main purposes of this study are to evaluate the use of GW on GRs to examine if there might be an ecologically and economically more beneficial way to keep the roof green, we used a prepared greywater simulation (PGWS) to measure green roof plants' responses to it. Two different greywater models, non-diluted prepared greywater simulation (N-D.PGSW) and 50% diluted prepared greywater simulation (%50-D.PGWS), were used for irrigation; while tap water (TW) irrigation and no irrigation (N-I) were the other two conditions to make the study more reliable.