A simple explanation of thermodynamic anomalies of metastable water is given by the functional integral model of random network. Phase diagram, density maximum, and stability limits of liquid water are discussed. Thermodynamic anomalies near stability limits are explained as due to the network fluctuation effects and the mean-field values of diverging exponents are derived. Spatiotemporal patterns of the network rearrangement dynamics are also analyzed. The energy fluctuation exhibits a 1/f-like non-Debye type relaxation behavior.