The maximum that can be added is however much it takes to satisfy the "Chlorine Demand" of the water. I think what you are referring to is "What is the maximum Free Chlorine residual of drinking water and still be deemed safe?". All that is needed is to have a Free Chlorine residual of 0.2 to 0.5 ppm. Beyond that the water will have an objectionable taste and odor.
For swimming pools the Free Chlorine residual should be 1 - 4 ppm. Above 4 ppm could be harmful.
Drinking water:
EPA has set a maximum contaminate level for free chlorine at 4 mg/l as residual, from the disinfection byproducts rule.
The sodium hypo chlorite brand that I use has a maximum dose rate of 84 mg/l as part of its NSF 60 listing. It is 12.5% so this results in a dose rate of 10.5 mg/l.
Hydrae
I found some information on the same sobject:
NATIONAL SPA AND POOL INSTITUTE
Suggested Chemical Standards for Swimming Pools
Free chlorine, ppm 1.0 - 4.0
Combined chlorine, ppm None
pH 7.2 - 7.8 (ideal range of 7.4 - 7.6)
Total alkalinity, ppm (for liquid chlorine, cal hypo, lithium hypo) 80 - 100
(for gas chlorine, dichlor, trichlor and bromine compounds)
100 - 120
Total dissolved solids, ppm->Not to exceed 1500 greater than at pool start-up
Calcium hardness, ppm 200 - 400
Cyanuric acid, ppm 30 - 50