Flow calculation (water & sewer )

Estimated per capita wastewater output per day X number of people served = daily estimated wastewater discharge. Generally speaking, multiply this figure by 3 to get rainy day flow. Check with your local authorities on the Code of Practice to find out what is the maximum allowable velocity, allowance for rainwater infiltration etc. Normally, a sewer pipe must be minimum 4" in diameter.

In my area it is 110 gallons per day per person / per day it may be different for special applications like elderly .Consult your local board of health for specs.

outflow is the same as inflow, water in waste out ,irrigation can be put on a separate meter to reduce outflow estimates

A lot of companies are saving money by putting out flow meters on their lines. They find the out flow is much less and inflow.

110 gpcd is a lot of wastewater flow. That is close to 2/3 of the typical gpcd water demand. Wasterwater flows are hard to project, and typically vary substantially for different communities. somewhere between 50 and 70 gpcd for 3.5 person home is not unusally in California. commercial source will vary based on type of use and can vary substantial based on source and locations, e.g laundromat can use up to 550 gpd per machine. Industrial sources vary even more and need to be specifically analyzed.