Use of electron-based microscopy in aqueous media has been held back because aqueous samples tend to suffer from water radiolysis and other chemical degradation caused by the high energy of incident electrons. Here we show that aqueous liquid pockets in graphene liquid cells at room temperature display significantly improved stability when using deuterated water, D₂O. Reporting transmission electron microscopy (TEM) experiments based on common imaging conditions, we conclude that use of D₂O outperforms adding radical scavengers to H₂O regardless of imaging details; it increases the lifetime of dissolved organic macromolecules by a factor of 2–5, and it delays by even longer the appearance of radiolysis-induced bubbles, by a factor of time up to 10. We quantify statistically the consequences of minimizing the electron voltage and dose and conclude that the D₂O environment increases sample longevity without noticeable sacrifice of contrast that is critical for direct imaging of weakly scattering organic macromolecules and biomolecules.