It all depends on what you have to size and you need to consider a simultaneous factor

for house water tank +- 25L/pers
until 1000 pers 80l/pers7day...

washing basin 0.15l/s
shower 0.15l/s
wasing machine 0.20 l/s...

sewage

toilet 90 l/min
shower 30 l/min...