Condensed matters (liquids, glasses and solids) can be overheated or stretched only up to a limit. Within mean-field approximation, this limit is the so-called spinodal. This is the final limit for overheating, and therefore it is a very important quantity for safety calculations wherever high pressure- high temperature liquids are involved. In temperature-pressure space the spinodal is represented by a curve, starting from the liquid-vapour critical point and decreasing with decreasing temperatures down to the negative pressure region. The determination of the spinodal is a very difficult theoretical and a more-or-less impossible experimental task. By extrapolating chosen quantities, one might get the so-called pseudo-spinodal, a limit close to the real one. Based on a recently developed method, the pseudo-spinodal pressure (for given temperature) of water and helium-3 are determined, using liquid-vapour surface tension, interface thickness and vapour pressure data. The method is already proven to be valid for Lennard-Jones argon (a simple fluid), for carbon-dioxide (a molecular fluid), for helium-4 (a quantum fluid), and the Shan-Chen fluid (a mesoscopic fluid).