Sa’ad Radiyallahu Anhu enquired from Rasoolullah SallalahuAlayhiWaSallam that as His mother was deceased, what type of Sadaqah would be best (for inviting Divine blessings for her soul?) Rasoolullah SallalahuAlayhiWaSallam replied that water was the best of all. On that Sa’ad RadiyallahuAnhu had a well dug, so that His mother will receive all the blessings.
Supplying water was considered as being the best Sadaqah, as there was scarcity of it in Madeenah Munawwarah. All hot countries suffer from shortage of water, but there was an acute shortage in Madeenah Munawwarah in those days.
Besides this, the benefits of water are common as well as its usage. A Hadeeth says that whoever arranges a water supply system, wherefrom men, jinns and birds drink, will keep on receiving the reward till the day of judgement, even after he dies.
Abdullah ibn Mubaarak (Rahmatullah Alayh) was visited by a person who complained about a wound on his knee. Despite continuous treatment by many physicians for the last seven years, it had not healed at all. Abdullah ibn Mubaarak (Rahmatullah Alayh) advised him to have a well dug at a place where drinking water was scarce and said “I have full trust in Allah I, that as soon as the water appears in the well, the wound will heal up”.
The famous Muhaddith Abu Abdullah Hakeem (Rahmatullah Alayh) had some wounds on his face, which remained incurable, in spite of various treatments for a year. He requested his teacher, Abu Uthmaan Sabuni (Rahmatullah Alayh) to make a Duaa for the cure of this wound. As it happened to be Friday, the teacher made a long Duaa, to which the whole congregation said Aameen. On the next Friday a woman came to the congregation and presented a written note which stated that, after she returned home last Friday, she kept on praying for Hakeem carefully and she saw Rasoolullah SallallahuAlayhiWaSallam in her dream telling her to advise Hakeem to make the arrangements of water to be supplied to the Muslims. After hearing this, Hakeem arranged drinking water at the door of his house for the way-farers and got the water regularly replenished along with some ice. Hardly a week had passed when all the wounds were healed and his face looked much more handsome than before
(Source: Fadhaail Sadaqaat-Hazrat Moulana Muhammed Zakariyyah (Rahmatullah Alayh)