Whether water used to wash impurity remains pure or not
3-4-2016 | IslamWeb
Question:
Assalaamu alaykum. If mathy (pre-seminal fluid) dried and we clean it with pure water, does it make the water impure?
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad 
is His slave and Messenger.
Mathy is impure, as we explained in fatwa 260293. If mathy dries up, it remains impure and the area stained with it is not declared pure simply because the mathy has dried up. Haashiyat Ad-Dusooqi reads, "Impurity is not removed if urine becomes dry, and therefore, if it touches a wet place, it renders it impure."
If water is poured over dry mathy, then its ruling is that of water that comes in contact with an impurity: if the water changes (in color, smell, and taste), then it is impure. If it does not change and the mathy is not removed, then it is still impure because it is a small amount of water (please, refer to fatwa 1373) that came in contact with an impurity. If the water does not change and the mathy is removed, then, according to one of the two reported views of the Hanbalis, it is pure. The Hanbali scholar Ibn Qudaamah 
wrote:
"The water used in washing an impurity and that then separates from it is divided into three categories:
First: the water changes after contacting the impurity. In this case, the scholars unanimously agreed that it is impure because the impurity changed it.
Second: the water does not change and the impurity is not removed. In this case, the water is impure because it is a small amount of water that came in contact with an impurity and did not remove it. The water separating from the impurity remains impure, just like the water that remains on it; and squeezing the water out of impure clothes does not make them pure.
Third: the water does not change and the impurity is removed. There are two scholarly views in this regard; the most likely correct of the two is that the water is pure. This is the view of (Imaam) Ash-Shaafʻi ... the second view is that it is impure; this is the view of (Imaam) Abu Haneefah." [Al-Mughni]
Allaah knows best.