Model water spectra of the 400 GHz lines in the case of U Her. The frequency is shown in the top row spectra in gigahertz. Each row of spectra corresponds to the mass loss rate indicated in the leftmost spectrum. The blue profiles correspond to r_e = 0.8 R and the red profiles to r_e = 0.1 R. The vertical scale, in Janskys, is different for each mass loss rate. The horizontal scale is in velocity (km s⁻¹). The strongest maser activity is found for Ṁ = 3 × 10⁻⁶ M_⊙ yr⁻¹ and is absent for the highest mass loss rates. The mass loss rate derived from the CO lines is 2 × 10⁻⁷ M_⊙ yr⁻¹.