Analysis of the water line emissions in L1157 B2. o−H₂O (3₁₂ − 3₀₃)/p − H₂O (1₁₁ − 0₀₀) ratio versus o−H₂O (3₁₂ − 3₀₃) (in logarithmic scale, top panel), o−H₂O (2₁₂ − 1₀₁)/o−H₂O (1₁₀ − 1₀₁) ratio versus o−H₂O (2₁₂ − 1₀₁) (middle panel), and o−H₂O (3₁₂ − 3₀₃)/o−H₂O (1₁₀ − 1₀₁) versus o−H₂O (3₁₂ − 3₀₃)/o−H₂O (2₁₂ − 1₀₁) ratios (bottom panel), for non-LTE (RADEX) plane-parallel models at the labelled temperatures. A linewidth of 5.5 km s^-1 has been assumed, according to the observed spectra. Each coloured curve corresponds to the labelled N_H2O (see insert at the top-left corner). H₂ density increases from left to right as the labelled values. Triangles with error bars indicate the size of the emitting region (30″, 15″, 3″).