Yes. I have a flock of over 50 chickens housed with 20 ducks, 2 geese, 14 guinea fowl, and 2 rabbits. All get along together with no problems, but my run is LARGE (100'+ long & 20+ wide). Just know that ducks will befoul any waterers they use. I change all my waterers daily in addition to filling basins and stock tanks for the waterfowl.
Do not brood chicks with ducklings or goslings, however. The latter two grow large even faster than chicks and they will create chick pancakes if you try to raise them together.
I got one hen who insists on living in the duck house. The ducks like her... but bite all other chickens. It's not that big a deal, but I have heard stories of ducks eatting chicks by chasing off the broody mom and then killing and even eatting the chicks. I'd be careful. But not impossible.
As always, depends on the bird and the space provided for everyone.
They are adults not chicks and my duck is extremley nice but i had another one and my cat ate it when they were little,so since then she has been by herself but im sure she wont hurt them.They have the right amount of space i think.
Should i empty some of the water just to be safe?
Depends on how deep your water is and how big your chickens are the water in my pool comes up to the belly of my chickens when they get in I swear my chickens love the pool it is the funniest thing I have ever saw