SB 10.24.8

śrī-nanda uvāca
parjanyo bhagavān indro
 meghās tasyātma-mūrtayaḥ
te ’bhivarṣanti bhūtānāṁ
 prīṇanaṁ jīvanaṁ payaḥ
śrī-nandaḥ uvāca — Śrī Nanda Mahārāja said; parjanyaḥ — the rain; bhagavān — the great lord; indraḥ — Indra; meghāḥ — the clouds; tasya — his; ātma-mūrtayaḥ — personal representatives; te — they; abhivarṣanti — directly give rain; bhūtānām — for all living entities; prīṇanam — the gratification; jīvanam — the life-giving force; payaḥ — (like) milk.
Nanda Mahārāja replied: The great Lord Indra is the controller of the rain. The clouds are his personal representatives, and they directly provide rainwater, which gives happiness and sustenance to all creatures.

Without clean rainwater, the earth could not possibly provide food or drink for anyone, nor could there be cleanliness. Thus it would be difficult to overestimate the value of rain.