AbstractWater maser emission has been detected only toward three planetary nebulae (PNe). In particular, in K3-35, the first PN where water vapor maser emission was detected, the components are located in a torus-like structure with a radius of 85 AU and also at the surprisingly large distance of 5000 AU from the star, in the tips of the bipolar lobes. The existence of these water molecules in PNe is puzzling, probably related to some unknown mechanism shielding them against the ionizing radiation. We report the detection of HCO⁺ (J = 1 − 0) emission toward K 3-35, that not only suggests that dense molecular gas (~10⁵ cm⁻³) is present in this PN, but also that this kind of PN can enrich their surroundings with organic molecules.