It is well known that the amount of ground water influences gravity. When the target is deeper, this requires a correction or will be present as noise in the data. However, hydrological information can be valuable, particularly in the large parts of the world with scarce fresh-water resources. The sensitivity of ground gravity measurements to ground water variations is high, but it is a challenge to cover large areas with microgravity data in an economic way.
Satellite measurements (GRACE) have high precision, but the lateral resolution is not better than a few hundred of kms. Such data can give a broad picture for a land or a continent, but not for practical use in smaller scale.
Jacob et al. (2010), Wilson et al. (2012), and Christiansen et al. (2011) all reported successful hydrology monitoring.
Subsidence can be a measure of ground water changes in areas of drought or aquifer over-exploitation (e.g. Murray and Lohman 2018).