This presentation will explore various possible approaches depending on the processing technique (cross-correlation – auto-correlation) or the studied wavefield (ballistic or coda waves). Highlighting recent advances and limitations, in the detection and quantification of hydrological variations across a range of controlled settings and scales, including laboratory experiments and both short- and long-term field observations. Particular emphasis is placed on the sensitivity of retrieved seismic velocity variations (dv/v) to fluctuations in groundwater levels and changes in the fluid of the unsaturated zone.