For Watershed reports, a county or state is considered to "contain" a portion of a watershed if any of the watershed's land area is located within the administrative unit's border (or within 0.1 miles of the border). A watershed is considered to contain a portion of a county if any of the county's land area is located within the watershed's border. County and state watershed data are calculated by summing or averaging over all watersheds the county or state contains.

Scorecard's Watershed reports generally identify more watersheds as contained within a county or state compared to Scorecard's Water Quality reports. This is because Scorecard uses a stricter definition of "contain" when it is analyzing Clean Water Act data for Water Quality reports. If 5% or less of a watershed's total area is not within a county or state, that watershed does contribute data for aggregation into Water Quality reports. Scorecard uses this stricter definition because it prevents watersheds that represent only a small fraction of a county from distorting county summary values for percent and number of impaired waterbodies.