For the more specialist jobs, we keep a huge range of waterproofing materials in stock, with more available next day from our network of suppliers. If you are looking for drainage filters, waterproof membranes, cavity trays or mastics and grouts. For the more specialist jobs, we keep a huge range of waterproofing materials in stock, with more available next day from our network of suppliers. If you are looking for drainage filters, waterproof membranes, cavity trays or mastics and grouts Longwater can supply everything you need.