It depends.
Do you have data on the following:
1) Number of properties connected
2) Total annual water consumption
3) Total billed quantity.
4) Month by month consumption
5) Sewerage flows (assuming the town is sewered)
6) Break down of consumption between residential , commercial, industrial.
7) Population serviced.
8) Maximum and minimum day demands.
9) System losses.

If you have some or all of that data then by manipulating it in various ways you should be able to get the information you require.
If you have none of this data then you have a couple of options.

1) Make some assumptions based on your experience , knowledge or gut instinct.
2) Find some figures in the various text books, planning guides etc.
3) Pick several properties at random through the city and read the meters there every day for several weeks.
4) Ask a neighboring city or utility .

As a very rough number you will probably be in the 60-100US gallons per day per person average range, but it also depends the on climate , the demographic , population density, and whether the town is old or if its newly developed.
For a peaking factor 2.5 would be a good starting point but smaller towns tend to have a larger but steeper peak when compared to larger towns and cities.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

Also, consider if the area has a lot of outdoor irrigation. As Ashtree said, a peaking factor of 2.5 is a good starting point, but if you are looking for the peak hour, I have seen as high as 6 for a mostly residential area in a dry climate where they really like their lawns.