Recent development of software makes much contribution in the form of easinessand speed to reach solution of scientific calculation, one of that contribution is in the modelling ofobservation data. Data of water (H2O) density is reference data which at a glance look like so linear withrespecto temperature but using CurveExpert 1.3 there was anevident that some other models which arenon-linear have higher level of accuration than the linear model itself. In this paper, using software calledCurveExpert 1.3 some non-linear models were presented and can be chosen as anaccurate model based onthe criteria that the standard error is close to zero and the coefficient of correlation is close to one. Somemodels 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
