  Density functional simulations of condensed phase water are typically
inaccurate, due to the inaccuracies of approximate functionals. A recent
breakthrough showed that the SCAN approximation can yield chemical accuracy for
pure water in all its phases, but only when its density is corrected. This is a
crucial step toward first-principles biosimulations. However, weak dispersion
forces are ubiquitous and play a key role in noncovalent interactions among
biomolecules, but are not included in the new approach. Moreover, na\"ive
inclusion of dispersion in HF-SCAN ruins its high accuracy for pure water.
Systematic application of the principles of density-corrected DFT yields a
functional (HF-r$^2$SCAN-DC4) which recovers and not only improves over HF-SCAN
for pure water, but also captures vital noncovalent interactions in
biomolecules, making it suitable for simulations of solutions.
