The accurate estimation of groundwater recharge is the key and a necessity for sustainable use of groundwater resources. This is especially true for phreatic coastal aquifers as the balance between the fresh and the saline water is more fragile. Excluding the “one time reserve”, the safe yield of a groundwater system must not accede, on the average, the average recharge. [Further, in most cases some flushing of the aquifer must also be kept to prevent...