Question 15: Some places in Saudi Arabia and in other countries recycle sewage water and reuse it to irrigate land and so on. Sewage water purification plants vary in their capabilities to filter impurities, and also in the types of companies which supervise these stations in Jeddah and Riyadh, for instance. After recycling the drain water which we are asking about, it becomes so pure that it is impossible to detect the difference between it and regular drinking water. Is this water pure? Can we use it in performing Wudoo’ (ablution), washing our clothes and body, removing Najaasah (ritual impurity) with it, and drink it?
Answer: If the reality is as you mentioned, that the sewage water becomes pure after recycling and purification so that the color, smell and taste of Najasah that contaminated it is removed, then it is Tahoor (pure and purifying) and does not defile anything it touches. It is permissible to use in irrigation, cleaning one’s body, place, clothes, performing Wudoo’ and Ghusl (ritual bath) following major ritual impurity, etc. It is also permissible to drink, unless it is proven that it is harmful to the health. In this case, it should be avoided to protect oneself from harm, not due to being Najis (ritually impure)... read more here.