The most notable shortcomings of water models (leading to known artefacts in biomolecular MD simulations, demonstrated in Fig. ) are the underestimated surface tension and viscosity, as well as the dielectric constant (see Fig. and the next section for a detailed discussion on the proper treatment of the dielectric response). Underestimated surface tension leads to incorrect phase behaviour and opening of pores at too low areas per molecule in lipid monolayer simulations. Too low viscosity leads to overestimated rotational dynamics of proteins as follows from comparison between simulations and experiments. The incorrect overall rotational diffusion can be corrected during analysis for folded proteins but not for disordered proteins or other biomolecules. Furthermore, incorrect bulk water properties usually imply inaccuracies in interactions between water molecules, which are likely to cause other problems in biomolecular simulations. Indeed, the commonly observed over-compact ensembles of disordered proteins have been related to inaccuracies in water models. In applications where the water viscosity or surface tension are critical, the optimal solution is to use a more advanced water model, which without careful reparameterization, however, could lead to inconsistencies with other parameters. In practise, such inconsistencies are observed to be less severe than issues arising from incorrect water properties. In conclusion, we are convinced that using modern water models with correct surface tension, viscosity, dielectric response, and other physical properties is a must for future MD simulations of biomolecules.