We report the detection, for the first time, of HCO+(J= 1→ 0) emission, as well as marginal CO (J= 1→ 0) emission, toward the planetary nebula (PN) K3-35 as a result of a molecular survey carried out toward this source. We also report new observations of the previously detected CO (J= 2→ 1) and water maser emission, as well as upper limits for the emission of the SiO, H 13 CO+, HNC, HCN, HC 3 OH, HC 5 N, CS, HC 3 N, 13 CO, CN, and NH 3 molecules. From the ratio of CO (J= 2→ 1) to CO (J= 1→ 0) emission we have estimated the kinetic temperature of the molecular gas, obtaining a value of≃ 20 K. Using this result we have estimated a molecular mass for the envelope of≃ 0.017 M⊙ and an HCO+ abundance relative to H 2 of 6× 10-7, similar to the abundances found in other PNe. K3-35 is remarkable because it is one of the two PNe reported to exhibit water maser emission, which is present in the central region, as well as at a distance of≃ 5000 AU from the center. The presence of molecular emission provides some clues that could help in understanding the persistence of water molecules in the envelope of K3-35. The HCO+ emission could be arising in dense molecular clumps, which may provide the shielding mechanism that protects water molecules in this source.