Sound Science Bite: October 4. An editorial in the 26 Sept 2014 issue of the journal Science titled "The Drought You Can't See" raises the issue of groundwater conservation. A scientific study appearing on page 1587 of that issue, reports on a new way of assessing the change in the amount of groundwater, the world's most used water resource. This study confirmed a massive loss of groundwater in the western United States, especially California.

Groundwater is contained in porous and permeable rock units called aquifers, and is usually accessed for human use by wells. The authors of the study used a network of Global Positioning System (GPS) sensors to calculate that the amount of groundwater lost in the western US due to the recent drought would cover that whole area in water 2.5 inches deep. The loss of water reduces the weight on the land and the land rises elastically in response. It is this rise, measured by GPS, they used to confirm earlier findings of groundwater depletion in California by the GRACE satellites that measure the pull of the Earth's gravity beneath them. The less the amount of water, the less mass, and the weaker the gravitational pull.

I use this story to address a probably widespread misconception about groundwater. Most people probably think the water under their land is theirs, to use however they desire, an idea that originated in English common law. State laws are often based on this idea. Surface water belongs to the state; groundwater belongs to the landowner.

The editorial quotes an Arizona congressman claiming that his state law declares surface water and groundwater are "decoupled", that is, they are separate entities. Not so. Fresh-water groundwater in aquifers is stored surface water, and most of it flows like the water in rivers and streams, albeit more slowly. The groundwater under a person's land today may have been under his neighbor's land some days previously. Extracting excess groundwater is pretty much the same as daming up a stream to deny water to those downstream.

State laws need to get in line with how nature actually works. Surface water disappears into the ground in a recharge zone and then into the aquifer. It can reappear in springs and artesian wells. If groundwater just sat underground, you wouldn't have springs or artesian wells, and your well would go dry pretty fast. Some groundwater, however, like the Ogallala Aquifer of the Great Plains, is considered non-rechargeable - or rechargeable at such a slow rate that when it is gone, it will be gone for good. California recently inacted a law to conserve groundwater - the last far western state to do so. Other drought-stricken states are dragging their heels. In Texas, for example, it is still lawful for a landowner to pump as much groundwater as desired, despite damage to other wells or to the aquifer. The only remedy to this, apparently, is groundwater management through local conservation districts. Groundwater is too precious to be mined indiscriminantly until it disappears.