The solubility of water in melts in the system NaAlSi3O8 – NaAlSiO4 – H2O has been determined up to 10 kb, essentially using the method of Kennedy et al. (1962). Because the gels used were extremely hygroscopic, however, a correction to the approximate solubility value obtained was made by determining the amount of moisture originally absorbed in the gel powders. Using this method, solubility data are simply obtained as by-products of the experimental runs made for the investigation of phase equilibria.The H2O-solubility in the melts is not too sensitive to a variation in anhydrous composition of the melts (~6 ± 1 wt.% H2O at 2 kb and ~11 ± 1 wt.% H2O at ~5 kb in the range of compositions Ab100Ne0 – An40Ne60). H2O-solubility in the (Anl) and (Ne) univariant melts was determined up to 10 kb (H2O contents: 4.7 wt.%/1.1 kb and 852 °C, 6.2 wt.%/2 kb and 804 °C, 10.8 wt.%/5.2 kb and 672 °C, 12.2 wt.%/6.6 kb and 655 °C, 13.2 wt.%/7.3 kb and 652 °C and 14 wt.%/10 kb and 632 °C). The origin of water bubbles in quenched hydrous glasses in this system is essentially attributed to the separation of the dissolved water from the melts upon quenching.This method was further extended to determine the H2O-content in hydrous minerals, analcite, nepheline hydrate I, and zeolite species P. encountered in this system. The results agree fairly well with data reported by previous authors.