The H2O – J index measures the strength of the 1.4 μm water feature using HST's WFC3 instrument in units of atmospheric scale height (H). The nine planets with strong measured water features (H2O – J > 1, blue squares) have Teq > 700 K and log g > 2.8 (dotted lines). The remaining five planets with H2O – J < 1 (red squares) have muted water features. The size of the squares is inversely proportional to the uncertainty in the H2O – J index, thus larger symbols carry more weight. Like the dotted lines, the dashed diagonal line also delineates these two "classes" of exoplanets. Within the left panel, the gray circles depict confirmed transiting exoplanets with known masses and radii. The coloring in the right panel depicts the best-fit 2D model segmented into four quadrants (yellow lines and numerals). Additional measurements are needed to more precisely determine the transition region for atmospheres with and without obscuring clouds/hazes at the depths probed by HST/WFC3.