To build the water storage underground we had to enlarge the space already available slightly.
We didn't suspect to encounter huge rocks which needed to be drilled away with pneumatic drill. Paco , the builder of our house, helped out by providing us with a man and a drill. It took him a whole day to remove two big rocks and level out the rest of the earth. We were collecting the rubble an wheelbarrowing it to the side. Our arms and legs were aching for another week after this and we still have a long way to go!