Recent development of software makes much contribution in the form of easiness and speed to reach solution of scientific calculation, one of that contribution is in the modelling of observation data. Data of water (H2O) density is reference data which at a glance look like so linear with respecto temperature but using CurveExpert 1.3 there was anevident that some other models which are non-linear have higher level of accuration than the linear model itself. In this paper, using software called CurveExpert 1.3 some non-linear models were presented and can be chosen as anaccurate model based on the criteria that the standard error is close to zero and the coefficient of correlation is close to one. Some models more accurate than the linear model resulting from CurveExpert 1.3 are Gaussian Model, Sinusoidal fit, Weibull Model, Hoerl Model, MMF Model, dan Harris Model. Keywords: density of water, non-linear model, CurveExpert 1.3. Entjie Mochamad Sobbich, Arminda Kastono; Pusat Penelitian KIM-LIPI
