The PO 3 - .(H 2 O) n clusters (n=1, 2, and 3) have been studied using ab initio quantum mechanical methods. Self-consistent field (SCF), configuration interaction with single and double excitations (CISD), and coupled cluster singleand double excitation (CCSD) levels of theory were employed in conjunction with basis sets of quality double-zeta (DZ), double-zeta plus polarization (DZP), and DZP plus diffuse functions. The most important finding is that the clusters prefer to form high-symmetry double donor-double acceptor hydrogen bonds between the PO 3 - anion and the H 2 O molecules