"You wash the parrot in water."
Translation:In aqua psittacum lavatis.
"In water" means a bath, so we can say bathing in Latin, or does it mean "with water", and in this case we could use "cum + ablative"? "to wash in water"
For instance, you wash your vegetable in water, you put them in a sink, and turn on the tap, so I think that cum + ablative would do, or the ablative of means, without any preposition.
Is it correct?
Actually, if you're using water for washing, you would not use the preposition cum ( = "with") in your sentence. That's because water is a 'thing,' as opposed to a person (or animal); and the ablative case alone (without the preposition cum) expresses the function 'thing by means of which/with which' the subject does the action. ( = ablative of means)
So: Aqua psittacum lavatis, "You all are washing the parrot with water." We don't have long marks (abl. aqua needs a long a for the final syllable); so it will be easier to see with this example: Vino psittacum lavatis, "You all are washing the parrot with wine." That's the ablative of means.
Keep "cum" for "together with people/animals" (Cum amicis ad urbem advenio, "I arrive at the city with friends") and for some 'manner' expressions, like magna cum laude, "with great praise" (she/he earned a college degree), and so forth.