well, a cistern Vin.i.139; Vin.ii.122; MN.i.80; AN.iv.171; Ja.iii.216; Ud.78; Pv.ii.7#8; Pv.ii.9#25; Mil.411; Vism.244 (in simile) DN-a.i.298; Vv-a.40; Pv-a.78.

uda + pāna lit. “(place for) drinking water”; cp. opāna, which in the incorrect opinion of Pāli Commentators represents a contracted udapāna