Water saving is significant in Islam. Reusing wastewater through the water treatment process focused on membrane water treatment technology is one of the ways to save water. However, discussions and debates among scholars and the community continue to occur because the source of this water treatment is obtained from mustacmal water (pure water but not purifying) and mutanajjis water (impure water that does not purify). In addition, the material for manufacturing membrane water filters is also a dispute in terms of halal or otherwise. Therefore, this study aims to identify the concept of water treatment and purification according to the perspective of Fiqh and science. Next, this study also studies the methods of membrane water treatment and purification and then evaluates the process of membrane water treatment from Fiqh perspective. This study uses qualitative research methods through document analysis and interviews with six experts in the field of Fiqh and water technology. This study found that there are special methods in the treatment of mustacmal and mutanajjis water. Combined, it will result in a water treatment method that aligns with shariah.