Figure 1.

Variation in leak density within metro areas (a) and the relationship between leak density and percent of leak-prone pipes across metro areas (b). See Table 1 for metro area abbreviations. The boxplots in panel (a) show the distribution of leak density among surveyed census tracts within metro areas. The numbers below the boxplots indicate the number of surveyed census tracts. Panel (b) shows the range of leak density observed among metropolitan areas, and the regression line illustrates that higher leak density is associated with greater percentages of leak-prone pipes.