A set of 7 offering bowls may be placed on one's shrine and filled with water daily as a way of accumulating virtue and merit.
Offering bowls are one of the basic practice in Vajrayana and other forms of Mahayana. Tibetan offer water first thing in the morning along with Serkyem filled with tea or wine, Butter lamp and conclude with Incense offering. It is a way to make offering to Buddhas and Bodhisattvas in four direction.
Buddhist practices emphasize seven bowls of water, representing the absolute purity of the Buddhas. Buddhas and enlightened deities obviously do not need the offerings, whether food, incense or water. The act of offering is for our own benefit, to show we think of our Bodhisattva vows first, that we wish to overcome attachments to these very things we offer. Water, without which there can be no life, is symbolic of our attachments and greed.