Your feed supply store will have vitamin and electrolyte powder mix. Usually I found it in yeast size packages and that worked great. Could buy it in strips of 3 packs and would be more than enough for newly hatched chicks and again used in heat of summer. In my new location it came in what's probably near half pound package. Let's face it, that's a bit much, as I looked for it just now in the cupboards to write down the name brand couldn't find it which is what I'm thinking is going to occur every time I need it. Was only $4-5 and with a long search to locate will probably last years.
I use it for less than first week of chicks life then fill a water fountain once or twice a week in dog days of August. You'll notice less feed intake during those few weeks when temps hit 90F, that's when I give some powder to water.