The Messenger of Allah, may Allah bless him and grant him peace, said: "The best charity is giving water to the poor." Narrated by Ahmad, Abu Dawud, al-Nasa'i, and Ibn Majah.
And on the authority of Abu Hurayrah, may Allah be pleased with him, the Prophet, may Allah bless him and grant him peace, said: "There is no charity greater in reward than water." Classed as hasan by al-Albani in Sahih al-Targheeb wa't-Tarheeb.