Vaisesika Sūtra 5.2.03

अपां संयोगाभावे गुरुत्वात् पतनम् ॥३॥

apāṁ saṁyōgābhāvē gurutvāt patanam ॥3॥

[अपाम् (apām) - of waters; संयोग-अभावे (saṁyoga-abhāve) - in absence of conjunction; गुरुत्वात् (gurutvāt) - due to gravity; पतनम् (patanam) - falling;]

Falling of water occurs due to gravity in the absence of conjunction.