Roe and Brooks developed a ten-step protocol for system preparation/equilibration. Check it out, especially their density fit in step 10:
Roe, D. R.; Brooks, B. R. A Protocol for Preparing Explicitly Solvated Systems for Stable Molecular Dynamics Simulations. J. Chem. Phys. 2020, 153 (5), 054123. A protocol for preparing explicitly solvated systems for stable molecular dynamics simulations | The Journal of Chemical Physics | AIP Publishing.