Grewal, Gwenda-lin. 2022b. “A Note on Plato’s Euthydemus 304b.” Classics@22: Poetic (Mis)quotations in Plato. Washington, DC: Center for Hellenic Studies. http://nrs.harvard.edu/URN-3:HLNC.ESSAY:102302586.
At Euthydemus 304b, Socrates seems to twist the famous first line of Pindar’s Olympian 1. Pindar’s line reads as follows:
Best, on the one hand, water, but gold as blazing fire
Here is Plato’s version:
But water <is> cheapest, being best, as Pindar said.
Even without the original or transposed context, Socrates has separated the words “water” and “best” in a way that “as Pindar said” cannot only refer to “being best”—for ἄριστον alone would be insufficient to recall Pindar’s verse. It is ὕδωρ and ἄριστον together that suggest the poem.  In addition, ὄν is not in the original line, so if this is meant to be a direct quotation, it already contains a modification. On the other hand, if the line’s sole purpose is to paraphrase, the implied sentiment seems odd. Unmodified Pindar sings that water is best, but does he somehow imply that water is cheapest? Or, does he imply that “though it is best, water <is> cheapest”?
As Pindar Said
The first three lines of Pindar’s ode laud water as best, and gold as akin to blazing fire, conspicuous at night and man-exalting, standing out in wealth. Later on in the poem, in lines 45–51, which recount what happened to Pelops, Pindar sings,
people did not, seeking you out far and wide, bring you to your mother,
immediately one of the jealous neighbors was secretly saying
that by fire of water (ὕδατος…πυρὶ)  at the boiling point
they cut you limb by limb with a sword,
and at the tables during the last course
they divided up your flesh and ate it.
It seems water is not incompatible with fire, or at least, it can come to be very hot under the influence of fire, and so become akin to fire. Where water boils Pelops’ flesh, in Clotho’s cauldron Pelops emerges, dazzling with a false shoulder that deceives as if it were the true original. Clotho reverses Pelops’ fate, his gleaming shoulder now furnished with ivory (26–7). But this very dismemberment was itself a rumor woven from jealousy that beguiles like a prosthetic limb. These words of caution swiftly follow:
of mortals over and above the true logos
may deceive, stories embroidered with dappled falsehoods. (28–9)
Embroidered stories (muthoi) seem to point to poetry as one of the wonders. Poetry has the power to spin lies that look uncannily similar to truths, and to deceive listeners with a tapestry of image. The fluidity of fire may be like water; a cauldron may bubble with watery flames. But as water and fire are dwarfed in brightness by the warm sun which shines by day, and ultimately by the contests at Olympia, which are celebrated in this victory ode, Pindar’s glorifying poem, too, is that which is glorified in and by the poem. This ode associates itself with those who carry the victory, and Pindar crowns the victor with a victory song. In the last lines of the poem, he offers this wish for the victor and himself:
and so long as I can with bringers of victory
to associate, being far-famed in wisdom by Greeks everywhere. (115–6)
But what about water’s victory? Water is best, but “Best of What?,” asks the title of W. H. Race’s 1981 article on Olympian 1. Where is the missing genitive that would explain water’s preeminence? Fire seems more praiseworthy, if for different reasons. Ancient scholia suggest that “of elements (στοιχείων)” should be supplied with “best”; later translators infer the presence of “of all things (πάντων).”  Water and fire may therefore remind listeners of Thales and Heraclitus.  But Heraclitus contains both in saying that the cosmos itself “was, is, and will be an ever-living fire” (DK B30); yet “different waters run different for those who enter the same rivers” (DK B12). Water and fire are dissimilar substances that yield a similarly evanescent permanence. Pindar boils them together and cites Clotho as the composer. Their opposition, on the other hand, is apparent in Nemean 1.20–5:
of a man who loves guest-friends, singing beautiful things,
for me there a fitting
dinner he’s arranged, and people often coming from elsewhere
the house is not unfamiliar with:
It is his lot to bring good [friends] against his slanderers, as water against
Scholars account for the other two elements—earth and air—by gold and ether, which are mentioned at lines 1 and 6, respectively.  And if other pre-Socratic contemporaries of Pindar are lurking in the background,  parallels to Parmenides’ Fragment 1 would be easy to see in chariots racing toward a victory. While Hieron of Syracuse, for whom this ode was composed, won in the single-horse race in 476 BC, Pindar looks forward to a new event, which Hieron would presumably also win, and so, which would give Pindar another occasion to sing:
with a swift chariot, discovering a helpful way of words
arriving at sunny Cronion. For me, then, in fact
a Muse nourishes the strongest shaft with strength.
Some are great at some things, others at others. (109–13)
In the Pindaric context, the “being” of the Olympic victors depends on the “thinking” of their celebrators, the poets. “The Muse loves to remember great contests” (Nemean 1.11–12). The athletes live on by being celebrated—gilded—rather than sinking into obscurity.  Yet the poets are themselves riders, and the victory ode another contest of skill. Who best sings the order of all things? Who lives on the most “far-famed” in wisdom? Water (the beginning of the poem) may be the way to get the crown of wisdom (the end of the poem), but one would have to be wise to know it. Perhaps wisdom is more akin to a charmed spring or way with words—molten poetry flowing into the poet from the Muses beyond. So in Olympian 6.82-6, Pindar sings:
which creeps toward me (I’m willing) with beautiful-flowing blasts:
my mother’s mother <was> a Stymphalian nymph, well-bloomed Metope,
who bore Thebe, driver of horses, whose lovely water
I drink, while weaving a tapestry of song for spearmen.
And in Nemean 7.61–3:
bringing true kleos to a beloved man, as streams of water,
I shall praise him: and this wage/reward (μισθὸς) is suitable to good [men].
In both passages, water’s flowing is an image for poetic inspiration.  The poet brings precious liquid from elsewhere, the reward or wage of kleos, which is also the song through which it is borne, which flows into the poet as running water.  But “warm water does not so softly wet / the limbs as the eulogy accompanied by a lyre” (Nemean 4.4–5). Water is best, but poetry better. The praiseworthy song bathes listeners in a temperate shower; it glides over the limbs smoothly, raining glory on both victor and poet. Water seems akin to the force of poetry in its most visceral sense, where performance and composition are one. The illusion that the poet has hold of the reins is the sign of poetic genius. 
As Socrates Said Pindar Said
Socrates may also have in mind Olympian 3.42–5, where the ranking of water reappears—
εἰ δ’ ἀριστεύει μὲν ὕδωρ, κτεάνων δὲ χρυσὸς αἰδοιέστατος,
νῦν δὲ πρὸς ἐσχατιὰν Θήρων ἀρεταῖσιν ἱκάνων ἅπτεται
οἴκοθεν Ἡρακλέος σταλᾶν. τὸ πόρσω δ’ ἔστι σοφοῖς ἄβατον
κἀσόφοις. Οὔ νιν διώξω: κεινὸς εἴην.
And if water bests, but gold <is> most revered of possessions,
now Theron, reaching forward, touches the utmost boundary
of Heracles by virtues of his own. What’s beyond is untrodden for the wise
and unwise. I won’t chase it: then I’d be the latter.