I was wrong to complain.*
Shahram emailed USGS and got this reply:
Public supply deliveries for Domestic use are in column V, with the tag DO-PSDel (DOmestic, PublicSupplyDeliveries). You can calculate the percentage of domestic use for public supply by dividing column V by column Q, PS-Wtotl (Public Supply total withdrawals).Go here to get state-by-state spreadsheets with county-level data.
Also read his previous guest post, where he discusses per capita use.
Bottom Line: Data is useless without knowing how to use it :)
* Now I am going to complain about these abbreviations: "DO-PSDel"? WTF?