The Left Over Wudu Water
It is reported in almost all the hadith collections that after completing wudu, the Prophet صلى الله عليه و سلم  used to drink the leftover water from the container. It has also been reported that he used to sprinkle some of the water on his tehband (lower garment). The Ulema have offered a variety of interpretations concerning the wisdom of these two practices. However Mufti Muhammad Shafi maintained that Sheikh al Hind`s explanation for these was the most insightful one.
According to his view, wudu is an action for ensuring the cleanliness and purity of the bodily parts. Yet, while it is important to purify the outward, it is even more important to purify the inward. So after completing wudu, the Prophetصلى الله عليه و سلم  performed these particular actions, both of which are connected to the matter of inner purity. The connection is that the two body parts involved here, the tongue and the private parts, go to the very foundations of humanity`s most negative trait and wrongdoings. Therefore, the Prophet صلى الله عليه و سلم  is recorded as having said:
He who guarantees that he will protect the following two: That which lies between his jaws (i.e. tongue) and that which lies between his legs (i.e. his private parts), I will assure for him of entry into Paradise.
Hence the purpose of drinking the water left over from wudu, and sprinkling some of it on one`s lower garment, is to focus attention on the importance of protecting against those two major sources of human deficiency.
(The Great Scholars of the Deoband Islamic Seminary by Mufti Muhammad Taqi Usmani Pg.20-21)