We have found evidence that water plugs in hydrophilic nanochannels can be at significant negative pressure due to tensile capillary forces. The negative pressure of water plugs in nanochannels induces bending of the thin channel capping layer, which results in a visible curvature of the liquid meniscus. From a detailed analysis of the meniscus curvature, the amount of bending of the channel capping can be calculated and used to determine the negative pressure of the liquid. For water plugs in silicon oxide nanochannels of 108 nm height, a negative pressure of 17 ± 10 bar was found. The absence of cavitation at such large negative pressures is explained by the fact that the critical radius for seeding cavities (bubbles) is comparable to the channel height. Scaling analysis of capillarity induced negative pressure shows that absence of cavitation is expected at other channel heights as well.