Amaroli is also referred to as Shivambu or Auto-Urine Therapy. Drinking urine for spiritual sadhana is said to increase the supply of Prana and Ojas.
Urine passed at any time of the day may be drunk, but the best urine is the mid-stream urine passed just after getting up in the morning. In Hatha Yoga Pradipika(#94 & #95) amaroli is described as the drinking of the mid stream amari (urine), leaving the 1st, as it is a mixture of too much bile and the last, which is useless. It is also referred to as Shivambu Kalpa in the Damar Tantra. The Hatha Yoga Pradipika is the better known of the two scriptures, so perhaps that is why amaroli is the term in common usage in the west.