Your question is far too general and unclear to answer.
Who are you setting standards for: A City, a County, a water district, a State ?
Are these standards for water demand or wastewater flows ?
Are there seasonal variations due to high irrigation demand or weather extremes ?
Who are the users: residential only, or commercial, residential, industrial, institutional?
Do you have, or can you obtain, actual measurements of existing demand? Can you develop a diurnal curve in which you can have reasonable confidence ?
If you have heavy industrial demands what are they and when do they typically occur ?
Are there nearby communities similar to yours who might have such data ?
What do you mean by "unit" and what is "N" in the formula you quote ?
Do not trust "standards" and handbook values, especially those developed by others for conditions you do not clearly understand. And don't develop standards for others to follow without making clear the conditions to which they apply, PLEASE!