I took that figure from the USGS per capita household water use[1], which was 300-380 liters per day. Watering plants may make up as much as 20% of that but the biggest culprits are toilets and showers. This report[2] directly measured 1000 households and found daily direct water consumptions from 456 liters to 1815 liters(jesus).

[1]: https://water.usgs.gov/edu/qa-home-percapita.html

[2]: http://www.awwa.org/portals/0/files/resources/water%20knowle...