Modular rainwater harvesting water storage tanks are constructed on site and made with crates that simply snap together and are stacked and placed in any configurations. The RMS modular rainwater storage tank system is wrapped in two layers of geo fabric material and rainwater liner. Tank size can vary in size from 500 gallons to any size storage. The RMS modular rainwater storage tank system is intended to be installed below ground and will meet H-20 load requirements.