Sa’d ibn ‘Ubadah reported: I said, “O Messenger of Allah, my mother has died. Shall I give charity on her behalf?” The Prophet, peace and blessings be upon him, said, “Yes.” I said, “Which charity is best?” The Prophet said, “A drink of water.
Source: Sunan al-Nasā’ī 3664
Providing clean drinking water through Solar Water Plants to people in need.