I'm not GQ, so I hope you don't mind my offering a reply... We, too, have Muscovies, as well as Anconas and a Buff Orpington. We bought a big ol' stock tank from Tractor Supply, thinking, "They're DUCKS! Of COURSE they want water to swim in!"
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Our Muscovies drink from tank, but it's the Anconas who live in it.
We have Muscovies who enjoy standing in the little pool (smaller than a kiddie pool), but none really care for a good swim.
Having said that, of course you should have water for them to drink and clean themselves in. If you only have Muscovies, though, I wouldn't go hog-wild on a fancy swimming set-up.
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Our Muscovies drink from tank, but it's the Anconas who live in it.

Having said that, of course you should have water for them to drink and clean themselves in. If you only have Muscovies, though, I wouldn't go hog-wild on a fancy swimming set-up.