Calcium 5-aminoisophthalate {[Ca(AlP)(OH2)(4)](H2O)}infinity (1), synthesized from Ca(OH)2 and HAP, exists as a double helix. Hydrogen-bonding interactions between metal-bound water molecules, carboxylate oxygen, and the -NH2 group result in the formation of a supramolecular assembly, where the double helices are connected to each other to form hexagonal channels filled with water molecules.