The percentage of potable water actually used for drinking and food prep is very small. Maybe 1 to 2 gal/day/person at most. Sanitary use is likely to be 10 to 15 gal/day/person. This is a typical rate for office workers where there would be limited use for toilets, hand washing, etc. A household can use up to 50 gal/day/person. The large increase in water use is attributed to bathing and clothes washing. Lawn watering and water makeup to a pool will add to this, but the amounts are seasonal and very site specific. Conservation measures would reduce all of these amounts.
As for reference sources, any good book on HVAC design should provide general guidelines as to water consumption on a per capita basis. These compilations of "rules of thumb" are often used for the initial sizing of utility systems when not much else is known about a project. Water agencies should be able to provide you with an estimate of water use distribution for their service area. Hope this helps.
Mike Callahan, PE