Falling groundwater levels are a problem, easy to monitor, difficult to solve. If the reason is indeed not overexploiting the aquifer by a local farm with irrigation pumps, the reason is probably less rain over a prolonged period. My professional background is hydrogeology and i did several studies in Burkina Faso to this phenomena. The results are not encouraging. Infilration rates with slopes less than 5% are in the order of 95% of the precipitation for larger catchments, so it looks ok, but only several rainy days may give a recharge through piping; percolation recharge in soil moistures is limited and liable to evapo(transpi)ration.
You just can hope that a next period will come with more rain, and levels will raise again for a while.
Best is to locate your wells in the scarce recharge areas, which are located along river beds, especially when the rivers are in hardrock and change course, which may indicate a fractured zone. Building some dams directly upstream of these wells may help, but make these dams extreamly strong, we had some dams just washed away with the 1 in 100 year flood that came the next year of course!
It goes without saying, that when you use handpumps, you better use a durable handpump like the Afripump, that does not need spare parts, see our website http://www.handpump.org