It is permissible to use the coconut juice for the ablution? Why?

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. We ask Allaah to exalt his mention as well as that of his family and all his companions.

It is not acceptable to perform ablution with coconut juice or rose water and the like, that is because the water that is pure and which purifies impurities is only the pure water which stays as it is created by Allaah whether it came down from the sky or sprung from the earth, and not the water which the trees have absorbed and which turned to another substance as it lacks the qualities of the original water. If this coconut juice is left unpreserved, it would decay and disintegrate, whereas the original water would stay as it is because it is pure.

Allaah Knows best.