piH-bonded complexes of water and the water dimer with ethene, propene, trans-2-butene, and allyl alcohol were examined in structures calculated ab initio at MP2/6-311++G(2d,2p). Cooperative enhancement of piH and sigmaH bonds is observed in the presence of hydroxy groups either from the second water or the alcohol. These interactions are analyzed in terms of structural changes, binding energies, normal-mode frequency shifts and intensity increases, and donor-acceptor charge transfers among local (natural bond) orbitals that nonadditively polarize participating bonds. The field effect of electron-releasing methyl groups attached to the double bond is also shown to strengthen the piH bond.