C

To solve the problem, we need to analyze the pressure differences in the capillary tube filled with water.
Step 1: According to hydrostatic pressure principles, the pressure at point y ($P_y$) is equal to the atmospheric pressure (P) since it is open to the atmosphere.
Step 2: For point x inside the capillary, due to capillary action and the curvature of the water meniscus, the pressure $P_x$ is lower than the atmospheric pressure.
Step 3: Therefore, we conclude that $P_x < P_y$.
Step 4: Given this relationship, the correct statements that could represent the pressure conditions in the capillary are summarized by the equality $P_x < P < P_y$ and we know that $P_y = P$.
Hence, the correct representation is given in Option C: $P_x < P_y$, which corresponds to $P$.
Thus, the relationships consistent with hydrostatic principles lead to the conclusion. Therefore, Option C is correct.