Water-divining in ancient India, or ancient Hindu method of detecting underwater, was based on vegetation, a useful indicator of groundwater both in arid and humid regions.
Sage Sarasvata wrote Darkargala, a geo-botanic guide for prospecting groundwater. He has pointed out that in an arid region, jujube and piu trees growing along with a date palm tree indicate groundwater, while in a humid zone, banyan occurring with ashvattha trees are indicative of water. Darkargala not only points to flora indicative of the presence of water but also to certain types of vegetation that indicate the absence of groundwater in a particular region; for instance, hollow and rough trees with shattered leaves point to the disappearance of water.
Varahamihira, an exponent of Darkargala, lived in Ujjayini (now Ujjain) in the 6th century CE. In his magnum opus, Brihatsamhita, certain fundamental laws of tropical ecology have been laid down to explain hydrological indicators in a mico-environment overlying groundwater reservoir in an arid or semi-arid region. With the help of bio-indicators, Varahamihira indicated groundwater at depths ranging from 8 feet to nearly 600 feet. According to him, termites make mounds in an area of high moisture content and a cool surface, indicating the presence of groundwater, and even a metallic deposit. Toxicity in water could be judged by the presence of these deposits, wrote Varahamihira. In Gir wildlife sanctuary (Gujarat), termite mounds in rugged terrain were helpful in locating groundwater. This indicator was also used for making a number of bore-holes for water in another hard-rock area of the state. These termite mounds, when combined with geophysical methods of Vertical Electrical Sounding, indicated a good underground water reservoir.
Varahamihira lists about 120 plants which serve as indicators of underground water.
This ancient Hindu geo-botanic exploration was noticed by Western scientists in olden days who used this method in another way, by taking notice of the reaction of some forked twigs on human beings. It was probably due to the absence of varied vegetation in Western countries that the account given by Hindu sages in Darkagala attracted the attention of their scientists.