Structural properties and stability of the Betaine-Urea natural deep eutectic solvent

•The minimum water content needed to prepare a metastable B:U:W NADES was in a ratio of 1:1:2.•The stability of a B:U:W NADES is highly dependable on the temperature and preparation time.•The addition of three water molecules increases the electron density of betaine’s carboxyl group.•The increase in the electron density generates resonance and stability of the system.•Computational studies showed a possible supramolecular structure of a stable B:U:W system.