My friend wants to make a water feature for her hubby's 50th birthday. We found a lovely old millstone at a reclaimation yard which hopefully will be the centrepiece but it's incredibly heavy (takes two burly men to lift it). I know we need a resevoir and grid but have no idea what size of each we need and whether or not, because the millstone is so heavy, it would be better to have the grid bigger than the resevoir. Are there any experts out there with ideas? Quite happy to forego the pebble pool look if there's a better alternative.