Reference for Thoughts like rain drop bubbles

This is probably all wrong given I don't speak Pali, but here comes some amateur sleuthing...

The pali for (SN 22.95) that Chris mentioned seems to have "udakapubbuḷaṃ" as the pali for water bubble. This term also appears in this parallel (MND 15) which appears to be a longer form for this sutta (Snp 4.15) in the section which has:

Once I wished a place to stay,
but all the world is essenceless,
turmoil in every quarter,
I saw no place secure.

Empthasis mine. Unfortunately there is no english translation for this longer parallel which might be a synthesis of SN 22.95 and Snp 4.15. I'd note that the translation comes from the Mahāsangiti Tipiṭaka Buddhavasse 2500 which is described as coming from a Princess in Thailand:

"The World Tipiṭaka is a gift of Dhamma for the World from Her Royal Highness Princess Galyani Vadhana Krom Luang Naradhiwas Rajanagarindra ... Proof-read and published in Roman script by the M.L. Maniratana Bunnag Dhamma Society Fund ..."

I'd also note that the pali for that parallel also has 'citta' mentioned many times unlike SN 22.95.

Anyway, thank you for asking this question since it led to reading of Snp 4.15 and Mnd 15!

These are not exactly what you've asked for, but they are somewhat related.

From SN 12.23:

"Just as when the gods pour rain in heavy drops & crash thunder on the upper mountains: The water, flowing down along the slopes, fills the mountain clefts & rifts & gullies. When the mountain clefts & rifts & gullies are full, they fill the little ponds. When the little ponds are full, they fill the big lakes. When the big lakes are full, they fill the little rivers. When the little rivers are full, they fill the big rivers. When the big rivers are full, they fill the great ocean. In the same way:

"Fabrications have ignorance as their prerequisite, consciousness has fabrications as its prerequisite, name-&-form has consciousness as their prerequisite, the six sense media have name-&-form as their prerequisite, contact has the six sense media as its prerequisite, feeling has contact as its prerequisite, craving has feeling as its prerequisite, clinging has craving as its prerequisite, becoming has clinging as its prerequisite, birth has becoming as its prerequisite, stress & suffering have birth as their prerequisite, conviction has stress & suffering as its prerequisite, joy has conviction as its prerequisite, rapture has joy as its prerequisite, serenity has rapture as its prerequisite, pleasure has serenity as its prerequisite, concentration has pleasure as its prerequisite, knowledge & vision of things as they actually are present has concentration as its prerequisite, disenchantment has knowledge & vision of things as they actually are present as its prerequisite, dispassion has disenchantment as its prerequisite, release has dispassion as its prerequisite, knowledge of ending has release as its prerequisite."

This is from the Dhammapada:

Dhp 121. Think not lightly of evil, saying, "It will not come to me." Drop by drop is the water pot filled. Likewise, the fool, gathering it little by little, fills himself with evil.

Dhp 122. Think not lightly of good, saying, "It will not come to me." Drop by drop is the water pot filled. Likewise, the wise man, gathering it little by little, fills himself with good.

From SN 35.203:

"When, monks, a monk lives and practices like this, it occasionally happens that, through a lapse of mindfulness, evil and unskilled states arise, memories and thoughts pertaining to the fetters. His mindfulness is aroused only slowly, but then he soon abandons that state, drives it out, abolishes it, puts an end to it. Just as if, monks, a man were to let fall two or three drops of water into an iron pot that had been heated all day, those few drops would soon be wiped out and vanish — in the same way it occasionally happens to a monk living and practicing like this... but he soon puts an end to it.

This is not from the Pali Canon, but rather, it's from Mahasi Sayadaw's discourse on the Bhara Sutta (from a selection of Mahasi's discourses entitled "Thoughts on the Dhamma"):

Becoming and Dissolution

A bubble bursts soon after it has been formed. A mirage conjures up an image of reality which disappears on close examination. There is absolutely no substance in either of them. This is common knowledge. As we know their true nature, so also must we know the true nature of the phenomena. When a meditator acquires knowledge of concentration through the observance of the dissolution of the Aggregates (khandha), he will discover that the known object and the knowing mind are all in a state of flux, now appearing, now vanishing. They are transitory. There is no essence or substance worthy to be named "mine" in them. They signify only the processes of becoming and dissolution.

— Discourse on the Bhara Sutta

Like effervescent bubbles

In one of my ten-day meditation courses I experienced the following: I could feel a hot, burning shape, not unlike a piece of shrapnel in the middle of my forehead. It was seemingly solid and three-dimensional. As I paid it attention it became white hot. Then it began to wriggle. As it disintegrated I had a terrible vision along with an emotion of terror. I dropped through a trapdoor! I was being hanged. The next moment I felt not only utter peace but something else. My entire being - certainly my physical body - seemed to be nothing but a mass of bubbles rising within me. It could be likened to effervescent bubbles rising in a bottle of lemonade. They came into existence and went out of existence at great speed. They arose and passed away, moving upwards as they did so. It was very pleasant. Time must have seemed to have stood still, because I was eventually brought back to 'worldly reality' when an assistant teacher tapped me on the shoulder. The meditation hall was empty. They'd all gone. I had simply been enjoying this wondrous phenomenon of 'arising and passing way.' I had never experienced this before, nor since, though I've undertaken fourteen ten-day Vipassana retreats and been practising now of over thirty-two years.

Sāriputta enlightened as sotāpanna in Vinaya. Mahā (1) Mahākhandhaka, then he enlightened as arahanta in Sutta. Ma. Ma. Dīghanakhasuttaṃ, which it's atthakathā gave the similitude of vedanā arising and vanishing as bubbles.

Another, In sāriputta's cannons, KN Cūḷaniddeso Mogharājamāṇavakapañhāniddeso, used the similitude of viññāṇakhandha as bubble as well.

So, sāriputta maybe one of monks who listening Phena Sutta (SN 22.95), then he described his arahanta-enlightening-moments to his students. Then at 1st saṅgāyanā, his students put his description into that ancient atthakathā and into that KN Cūḷaniddeso which authored by sāriputta.

Also, in KN Dhammapada's atthakatha Dha.A.6 atta-kodhavagga Buddhavaggavaṇṇanā 2. Yamakappāṭihāriyavatthu. (149), there are the sāriputta's conversation with the buddha about he is a genius who can count every rain's drops into the ocean, mountain, and the ground.

This is closest I could get:

“So I say to you – This is how to contemplate our conditioned existence in this fleeting world:” “Like a tiny drop of dew, or a bubble floating in a stream; Like a flash of lightning in a summer cloud, Or a flickering lamp, an illusion, a phantom, or a dream.” “So is all conditioned existence to be seen.”

It was said to Ven. Subhuti.

Its chapter 32 of the diamond sutra.

I haven't found it.

Perhaps it's the Phena Sutta (SN 22.95):

Now suppose that in the autumn — when it's raining in fat, heavy drops — a water bubble were to appear & disappear on the water, and a man with good eyesight were to see it, observe it, & appropriately examine it. To him — seeing it, observing it, & appropriately examining it — it would appear empty, void, without substance: for what substance would there be in a water bubble? In the same way, a monk sees, observes, & appropriately examines any feeling that is past, future, or present; internal or external; blatant or subtle; common or sublime; far or near. To him — seeing it, observing it, & appropriately examining it — it would appear empty, void, without substance: for what substance would there be in feeling?

That's not given to Sāriputta, though, and it's about "feelings" rather than "thoughts".

More specifically related to thoughts (still not Sāriputta though, and no "body of water"), is Itivuttaka 87

One who stops such trains of thought
As a shower settles a cloud of dust,

That's the word vitakka for "thought".

Re. the "body of water" I think that Nibanna is sometimes compared to the ocean (but so is samsara).

In AN 10.15 the ocean is also used as a simile for "heedfulness" being the root of all skilful virtues.