S. R. Faruqi:

With regard to both structure and theme, this verse is one in a thousand. The meaning of 'in a flowing river, wash your hands' is 'take advantage of some common benefit'. Thus beauty (or the beloved) is a common benefit, you too should profit from it. In this way the beloved is a kind of individual (or thing) that's within the reach of everybody. The wordplay of 'moving/flowing water' and 'in a flowing river' is obvious.

In calling beauty 'moving/flowing water' there's also the point that the way water flows on and passes away, in the same way beauty too is a transitory thing: today it exists, tomorrow it doesn't. Therefore today, when beauty is present, take advantage of it. Tomorrow this beauty will flow away like water, or its level will sink like that of a river. (Today there's a flood, the water has risen wonderfully high; or there's an abundance of water because it's the rainy season; tomorrow, when things dry up, the water level will sink.) That is, beauty will decay.

In 'moving/flowing water' another point is that moving water is pure. There's a Persian saying, aab-e ravaa;N paak ast ; thus to be absorbed in the worship of beauty, or to dive into the river of beauty, won't cause any pollutedness, but rather can bring about purity.

In 'moving/flowing water' a third point is that earlier generations were acquainted with the Greeks' image of time as resembling a river. They would also have known the saying of Heraclitus that 'One never steps into the same river twice'. Thus however many times we descend into the river of beauty, we'll receive a fresh pleasure, because a river keeps renewing itself at every moment.

From the mystical point of view, it's common to call the (divine) beloved an 'ocean of beauty'. Nasikh has an extremely fine verse:

mire ma;hbuub se aa;Gosh ko))ii bhii nahii;N ;xaalii
vuh ba;hr-e ;husn aisaa hai kih ((aalam us kaa saa;hil hai

[no one at all is devoid of the embrace of my beloved
that ocean of beauty is such that the world is his shore]

But to call a human beloved a 'moving/flowing river' is a supreme idea.

Atish has, by calling existence and being a 'fathomless river', created a new aspect; and in the second line the metaphor and the image are such that-- praise be to God!

ba;hr-e hastii saa ko))ii daryaa-e be-paayaa;N nahii;N
aasmaan-e niil-guu;N saa sabzah-e saa;hil kahaa;N

[there's no fathomless river like the ocean of existence
the blue-like sky, the greenery of the shore-- where?]

[See also {320,4}; {1882,5}.]

FWP:

SETS == FILL-IN; IDIOMS
MOTIFS
NAMES
TERMS

I've seen the proverb with mu;Nh instead of haath , and sometimes with ga;Ngaa instead of daryaa , but such small variations just show how widely known it is. In the uses I've seen, it also seems to have the sense of 'act while opportunity offers'.

The word ;hukm does wonderful things to the first line. Of course it can mean simply 'effect', as we eventually conclude that it chiefly does in this case; but that meaning is secondary to its range of primary meanings related to authority and command (see the definition above). And in the ghazal world we're entirely accustomed to find 'beauty' as a dictator, an imperious issuer of orders of all kinds. So the first line becomes intriguing: does flowing water have some kind of power or authority that is governed by beauty, or might its power carry us off the way beauty sweeps away (and drowns) the lover?

Since our minds are busy teasing out such nuances and possibilities about the power of beauty, the second line comes as an entire surprise. It consists of a common proverb, which offers its own shock of recognition-- and which wipes away all questions of beauty's power and authority. In the proverb, it turns out that beauty is like a river, a 'common benefit' as SRF says, quietly flowing along, available to everybody; you'd be a fool not to take advantage of it by using it to wash your hands.

And yet, and yet. The very plainness and (cynical?) pragmatism of the proverb provoke us to look through and beyond it. There's more to a flowing river than the chance to wash your hands. There's its sheer beauty, its life-enhancingness (its thirst-quenching, its fish, the greenery along its banks), its dangerousness (floods during the rainy season, fear of drowning, crocodiles), its vulnerability (during the dry season), its mysterious combination of total elusiveness and movement (as Heraclitus observed) with stasis (even as its water constantly flows away, the river itself remains right there in its bed).

So perhaps having access to beauty is as valuable (and multivalent) as having access to a flowing river? The very simplicity of the verse finally renders it undecideable, it becomes what I call a 'fill-in' verse, since it can really be imagined to say about beauty almost anything that you want it to say.