Abstract Validation results for mass estimates measured by GRACE (Gravity Recovery and Climate Experiment) and GRACE‐FO (GRACE Follow‐On) currently hold uncertainties exceeding 10 gigatons (Gt), due to errors in auxiliary models and leakage noise from surrounding hydrological signals. Here, we propose the Lakes Nasser–Toshka in the Sahara Desert as an easily accessible benchmark that could remarkably reduce the validation uncertainty to several gigatons. We evaluate the 2002–2025 GRACE(‐FO) line‐of‐sight gravity difference (LGD) record against water storage derived from satellite altimetry and optical imagery. The results show that the measurement uncertainties for GRACE KBR (K‐band Ranging), GRACE‐FO KBR and GRACE‐FO LRI (Laser Ranging Interferometer) are 7.76 Gt, 5.46 Gt and 4.35 Gt, respectively. The GRACE‐FO LRI LGD interquartile range (0.166–0.493 nm/s2) establishes a performance benchmark for future LRI‐based missions. Lakes Nasser–Toshka offer a rare natural benchmark for in‐orbit commissioning and evaluating future satellite gravimetry missions.