11,20-Dihy-droxy-3-oxopregna-1,4-dien-21-oic acid monohydrate.

The title compound, C(21)H(28)O(5)·H(2)O, is the hydrate of a steroid derivative and was obtained by degradation of solid prednisolone sodium phosphate. The six C atoms in ring A are nearly co-planar with a mean deviation of 0.015†à . Rings B and C are both in chair conformations, while ring D has an envelope form. In the crystal, inter-molecular O-H⋯O hydrogen-bonding inter-actions occur between the hy-droxy groups, carbonyl O atoms and solvent water mol-ecules, resulting in an overall three-dimensional structure.