1litre=0.22 gallons approx. 1000ml=1000cc=1litre. 1cm=1/100m, so 1cc=1/1000000=0.000001m³. 1litre=0.001m³=0.22 gallons, 1m³=220gallons (a closer approximation would be 219.97)
Volume of sphere=(4/3)π×8=32π/3m³.
Volume of 100 spheres=3200π/3m³=3200π/3×219.97gallons.
This is about 737127 gallons. So the amount of water left is 212873 gallons approx.