There are only two wormers that I've ever added to water and one of them isnt sold anymore.
The problem with mixing a wormer in water is that you dont know if a bird will drink enough of it, or enough to be effective, or drink it at all. Sick wormy birds wont drink. Birds drink less in cooler temperatures.
It's best that birds are wormed orally one at a time. That way you know they got properly wormed and there's no guesswork about it. There are various way you can worm 50 birds or more.
There's nothing saying that you have to worm all of them in one day.
You can worm them by breed:
The first day worm your Barred Rocks, RIR's and Buff Orpingtons.
The second day worm your Sex Links and EE's.
The third day worm the rest of them and your barnyard mixes etc...
The best way to worm your birds is to snatch them off the roost early in the morning and have someone hold the bird for you. Then use your preloaded syringe using Valbazen to dose each bird individually. Dosage is 1/2ml given orally. Just pull the wattles down and the hens mouth will open. Then shoot the liquid in her mouth and quickly let go of the wattles so's she can swallow the liquid on her own. If you dont immediately let go of her wattles, she could aspirate.
Then get your next bird and repeat the procedure until finished.
If all your birds are the same breed, Use a black magic marker and mark both sides of the comb indicating that the bird has been wormed. Do this to all birds that you have wormed.
If the dont have a comb or the comb is too small, mark their legs.
If your birds are in different coops; worm one coop of birds one day, another coop the next day, another coop the third day etc...
Then reworm your birds in 10-14 days to kill worms hatched from eggs missed during the first worming.