Translation:The ducks do not swim when the pool has no water.
I am German, and when I translate the second part word by word into German without changing anything: "... wenn das Schwimmbecken kein Wasser hat." it is perfect. Nonetheless, the Danish sentence confused me, since I haven't seen such a word order before in Danish sentences here on Duolingo.
I just started reading some books in anish, and every once in a while they invert the order of the words, away from all inversion rules.
Thus, my understanding is that your suggestion is correct, and it would be the simple way of writing. However this rearrangement is also fine.
As far as I understand it, this Danish sentence is absolutely correct!
It consists of a main clause "Ænderne svømmer ikke..." and a subordinate clause "...når svømmebassinet intet vand har". Subordinate clauses require the syntax to differ.
I do not eat the apple = Jeg spiser ikke æblet
... because I do not eat the apple = ... fordi jeg ikke spiser æblet
Certain words (here "ikke" will be placed before the verb in subordinate clauses. It seems that the word "intet" causes the "intet vand" to go before the verb.