Water tracers in climate and earth system models provide a way to directly determine the geographic sources and sinks of moisture in the atmosphere. This can provide new insights into global and regional hydroclimate, and help determine the value of certain variables that are difficult to quantify otherwise, such as the moisture recycling ratio or advective length scale. However, water tracers are purely theoretical constructs, which means they cannot be directly validated against observations. To help rectify this issue, water isotopes, which are sensitive to the physics that control atmospheric moisture, can be used as a secondary constraint. This is especially true now given the growing proliferation of water isotope observations, particularly from satellites. This talk will present an example of using water tracers and isotopes to better understand a meteorological feature known as an "atmospheric river", and what the resulting analysis reveals about the underlying physics of the model being used (the Community Atmosphere Model Version 5 - CAM5). Finally, if time allows additional water tracer and water isotope modelling studies will be presented, including results from the newly developed CAM6 model, and what this new model reveals about the underlying controls of water isotopes in the atmosphere.