Effects of varying the HO abundance, the turbulence velocity, the temperature power law exponent and the velocity power law exponent on the normalized line strength are shown for o-HO (1_1,0 − 1_0,1). The standard model is represented by the red line in each panel, it has its values given in Table 1 and f_H2O = 4 × 10^-4. The short-dashed purple and the long-dashed green represent models with respectively: f_H2O = 1 × 10^-4 and 1.6 × 10^-3 in the first panel; υ_turb = 0.8 and 2.0 km s^-1 in the second panel; ϵ = 0.2 and 1.1 in the third panel; and β = 1.5 and 10 in the fourth panel. All other parameters have the same value as the standard model. We note that varying υ_turb has the effect of a line shift.