When a shower is served by
more than one showerhead, the combined flow rate of all
showerheads and/or other shower outlets controlled by a
single valve shall not exceed 1.8 gallons (6.81 L) per
minute at 80 psi, or the shower shall be designed to allow
only one shower to be in operation at a time in compliance
with the California Energy Commission - 2015
Appliance Efficiency Regulations (CCR Title 20, Article
4, Section 1605.3[h][5])