The paver are concrete, the liner is 5mm thick polyurethane (idk the spelling) with underlayment of 5mm thick pool liner and 6mm thick yoga mats, the filtration will be a DIY filter I made followed by a pond filter I brought from a local pet store. Plus the top pond with the minnows will have soil in it and a bunch of plants and the big pond will have a bunch of plants in the pond. As for overflow the top pond will over flow to the bottom pond which will have 10mm gap to the surface. And the pond area is mostly shelter from the common southerly rains we get in New Zealand