diff --git a/R/read_waterdata_samples.R b/R/read_waterdata_samples.R
index f6d45b0f..66e00578 100644
--- a/R/read_waterdata_samples.R
+++ b/R/read_waterdata_samples.R
@@ -509,10 +509,13 @@ read_waterdata_samples <- function(
 #' This function creates the call and gets the data for discrete water quality samples summary data
 #' service described at <https://api.waterdata.usgs.gov/samples-data/docs>.
 #'
-#' @param monitoringLocationIdentifier A monitoring location identifier has two parts,
-#' separated by a dash (-): the agency code and the location number. Location identifiers should be separated with commas,
-#' for example: AZ014-320821110580701, CAX01-15304600, USGS-040851385. Location
-#' numbers without an agency prefix are assumed to have the prefix USGS.
+#' @param monitoringLocationIdentifier A single monitoring location identifier
+#' with two parts, separated by a dash (-): the agency code and the location
+#' number. Examples: USGS-040851385, AZ014-320821110580701, CAX01-15304600.
+#' The summary service accepts only one site at a time; supplying a vector of
+#' length > 1 raises an error. The agency prefix is required: bare location
+#' numbers (e.g. "040851385") are accepted by the service but return an empty
+#' result.
 #' @export
 #' @return data frame with summary of data available based on the monitoringLocationIdentifier
 #' @rdname summarize_waterdata_samples