Cochrane reviewed two trials on dietary restriction to decrease bedwetting. A low antigen diet restricts diary, gluten, eggs, and most meats. A small trial showed an improvement with dietary restriction but a relapse occurred in 6/9 children given test foods compared with 0/9 given placebo foods. The second trial of dietary restriction only had one patient at the end of the trial dry with a high drop out rate.
My thoughts: Chances are you are already having hydrating and voiding “power struggles” with your child. I would avoid adding another conflict when there is poor evidence to support it. (Sample size was too small.) This is a very limited diet with a high drop out rate.
Huang, T., Shu, X., Huang, Y. S., & Cheuk, D. K. (2011). Complementary and miscellaneous interventions for nocturnal enuresis in children. Cochrane Database of Systematic Reviews. doi:10.1002/14651858.cd005230.pub2