Every drop tells a story: a new technique for dating water.

important to know the age so you can assess the susceptibility of drinking water supplies to surface contamination. If you know that the groundwater in a particular area fell 10 years ago as surface rainfall, you can then decide how long it will take a surface contamination to reach the water supply. " Plummer says that information on groundwater age, or the average time since the molecules were removed from the atmospheric cycle, provides a " fourth dimension " to hydrologic investigations, allowing scientists to observe spatial variations in water composition and relate these variations to the time of recharge. By determining water age at specific points in a hydrologic system, Plummer says, it is possible to estimate how quickly an aquifer can replenish itself. According to M. Lee Davisson, group leader of environmental chemistry and toxicology at the Lawrence Livermore National Laboratory Health and Ecological Assessment Division, water dating is also important because it can give a much clearer picture of how quickly a groundwater supply is replenished and thus how heavily the supply can be used. In practice, Davisson says, several ages would be generated over the aquifer area and calculated into a mean age for the entire water volume. If the water in a given aquifer Innovations n the face of it, calculating the age of water seems like an exercise best suited to academia. After all, what difference does it make to us if the water we're using fell in last week's rainstorm or in a storm 500,000 years ago? As it happens, it can make a great deal of difference.