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Here we aim to characterise submillimetre water masers at 437, 439, 471, and474 GHz towards a sample of evolved stars.  We used the Atacama Pathfinder Experiment (APEX) to observe submillimetrewater transitions and the CO (4-3) line towards 11 evolved stars. The sampleincluded semi-regular and Mira variables, plus a red supergiant star. Weperformed radiative transfer modelling for the water masers. We also used theCO observations to determine mass loss rates for the stars.  From the sample of 11 evolved stars, 7 display one or more of the masers at437, 439, 471, and 474 GHz. We therefore find that these masers are common inevolved star circumstellar envelopes. The fact that the maser lines aredetected near the stellar velocity indicates that they are likely to originatefrom the inner circumstellar envelopes of our targets. We tentatively link thepresence of masers to the degree of variability of the target star, that is,masers are more likely to be present in Mira variables than in semi-regularvariables. We suggest that this indicates the importance of strong shocks increating the necessary conditions for the masers. Typically, the 437 GHz lineis the strongest maser line observed among those studied here. We cannotreproduce the above finding in our radiative transfer models. In general, wefind that maser emission is very sensitive to dust temperature in the linesstudied here. To produce strong maser emission, the dust temperature must besignificantly lower than the gas kinetic temperature. In addition to runninggrids of models in order to determine the optimum physical conditions forstrong masers in these lines, we performed smooth wind modelling for which wecannot reproduce the observed line shapes. This also suggests that the masersmust originate predominantly from the inner envelopes.

Submillimetre water masers at 437, 439, 471, and 474 GHz towards evolved stars. APEX observations and radiative transfer modelling