Is it obligatory to access well water if one can reach it without harm?
Chapter on Tayammum
Al-Mughni
Book of Purification
Primary text
If a person finds a well and can reach its water by descending without harm, or by using a bucket or a garment to fetch it, descending or fetching is obligatory upon him. This obligation remains even if he fears missing the prescribed time for prayer, because engaging in obtaining the water is treated similarly to engaging in performing ablution (wudu). This ruling applies to one situated on a vessel in water, treating him as one who found a well.
Supporting text
If accessing the water requires hardship or risking one's life, then the person is considered to be without water (like one who cannot find water).