While the consequences of humidity during solid-state processing of sodium potassium niobate-based lead-free piezoelectric powders are well established, the effect of humidity at later fabrication steps is less known. This study assesses the effect of humidity on the sintering and functional properties of 0.06LiNbO3-0.94(K0.5Na0.5)NbO3 (LKNN). Samples sintered in high-humidity air display a higher density, lower dielectric losses, and an increased mechanical quality factor. The observed properties persisted even after five months of storage with marginal reduction in the measured piezoelectric parameters. While the improvements shown with the high-humidity sintering method might be too small to justify investments in special atmosphere sintering, it more importantly indicates that no special equipment or atmosphere control is required to avoid adverse effects of humidity during sintering of sodium potassium niobate-based piezoceramics.