Only in phrase opāna-bhūta (adj.) a man who has become a welling spring as it were, for the satisfaction of all men’s wants; expl^d. as “khata-pokkharaṇī viya hutvā” DN-a.i.298 = Ja.v.174
■ Vin.i.236; DN.i.137; MN.i.379; AN.iv.185; Vv.65#4; Pv.iv.1#60; Ja.iii.142; Ja.iv.34; Ja.v.172; Vb.247; Mil.411; Vism.18; Vv-a.286; DN-a.1177, DN-a.298.

o + pāna fr. pivati. Vedic avapāna. The P. Commentators however take o as a contracted form of udaka, e.g. Bdhgh. at DN-a.i.298 = udapāna