The thriving Chinese BeiDou Navigation Satellite System (BDS) and European Galileo are considered as new potential for precipitable water vapor (PWV) retrieval in order to support meteorological applications. Currently, some Low Earth Orbit (LEO) satellites which have the same function as navigation satellites can also contribute to atmospheric parameter estimation. Compared to Global Navigation Satellite System (GNSS) in high and Medium Earth Orbits (GEO and MEO), LEO navigation satellites are closer to the earth thus having the advantage of less path loss, stronger signals and faster movement. Therefore, the combination of high-, medium- and low-earth orbit navigation satellite constellations can be expected to contribute an improved performance of atmospheric water vapor retrieval. In this study, we developed a method of PWV retrieval based on multi-GNSS and LEO observations. The performance of PWV derived from BDS-only and Galileo- only data using precise point positioning (PPP) approach is carefully investigated and evaluated. The potential of combining GPS, BDS, Galileo, GLONASS and LEO observations for PWV retrieval is also assessed. Based on the results derived from the observations of Hongkong and International GNSS Service (IGS) networks, we can conclude that the BDS-only and Galileo-only PWV series agree well with GPS series in general, they both potentially contribute to meteorological applications. Thanks to the simulated LEO navigation observations, an improved accuracy of PWV estimates can be achieved with the combined method. Furthermore, a lot of accurate slant tropospheric delay (STD) are estimated during the data processing with LEO integrated, which will be of great benefit to obtain the slant water vapor (SWV) and contribute to the numerical weather prediction (NWP).