The WaterWatch Summary Table provides a synopsis of streamflow conditions for each day. The table is divided into two parts: a summary of the percentage of streamgages in each WaterWatch percentile class (appearing to the left of the "Total stations" column), and a percentile summary (appearing to the right of the "Total stations" column). The seven percentile classes are defined as follows:

1 = Lowest ever at a streamgage
2 = < 10th percentile
3 = 10th to 24th percentile
4 = 25th to 75th percentile
5 = 76th to 90th percentile
6 = > 90th percentile
7 = Highest ever at a streamgage

The number appearing in each class category is the percentage of the total number of streamgages with a flow in that class. As an example, consider the following table entries.

United States

                  Percentage in class (Driest to wettest)

                                               Total       Percentile summary
Date         1    2    3    4    5    6    7 stations    min  25th  50th  75th   max
20060329     7   23   20   41    7    2    0    3278    0.91  7.86 25.00 48.42 98.55

On March 29, 2006, 7 percent of the 3278 stations reported the lowest streamflow ever observed; 23 percent of the 32788 stations reported streamflow below the 10th percentile; 41 percent reported “normal” streamflow (25th-75th percentile); etc.

The second component of the table provides a summary of the observed percentiles for all stations. For example, on March 29, 2005, a percentile value was assigned to each of the 3278 streamgages based on the historical streamflow database for each streamgage. Of all 3278 streamgages, the “driest” streamgage had a flow value at the 0.91 percentile when compared to all flow values in the historical record for that streamgage. The “wettest” streamgage was at the 98.55 percentile when compared to all historical flow values for that streamgage.

Similarly, the median (50th percentile) value for the 3278 streamgages was 25.00, meaning that one-half of the streamgages had streamflow values above the 25.00 percentile, and one-half below. A median streamgage percentile value of 50 would indicate a balance between streamgages reporting higher and lower than normal conditions, so the 25.00 value indicates that many more streamgages are experiencing lower streamflows than are typical for this date.