Winter storms have filled California’s reservoirs and built up a colossal Sierra snowpack that’s nearly twice its normal size for this time of year. But years of dry conditions have created problems far beneath Earth’s surface that aren’t as easily addressed.

Groundwater — found in underground layers containing sand, soil and rock — is crucial for drinking water and sustaining farms. During drought years, 60% of California’s annual water supply comes from groundwater. This water is not easily replenished, especially as many groundwater basins across the state are critically overdrafted.

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