Sand was recently added as a finalist for entry into the National Toy Hall of Fame. As with many children, the material was a go-to toy for Thomas Mackisack, who combined it with another element for his childhood play. "I would spend hours trying to create intricate tunnels, absolutely fascinated by the way water could flow down the paths I laid," Mackisack writes, "only to eventually flood the pit and subsequently, my mother's neighbouring garden."

Now an Industrial Design student at New Zealand's Massey University School of Design, Mackisack revisited the idea of incorporating water into play with his Aqua Stack project. "Some of the frustrations with playing in the sandpit were mainly around water, getting it to the sandpit and controlling it," he writes. "Finding a way to contain and construct water became a starting point for the design. Additionally, finding a way to reuse the same water."

"Material choice was dictated by water. Due to the type of chemicals and processes required to make wood waterproof, I looked to plastics, exploring the potential of recycled material. I propose this toy would be injection moulded using Ocean Waste Plastic; creating a story of how a toy made from waste floating in the ocean, can have another life in better waters."

"The resulting toy is Aqua Stack. With endless potential for all little builders, the various block sizes can start upside down and stacked without water, forming an understanding of building. When ready, they can flip them over and stack them high, creating beautiful little water falls. Aqua Stack teaches simple physics principles around water pressure and gravity. Through slides, unstructured play can be expanded, and the mounting system enables accessorises like dam walls, sieves and water wheels. Additionally, the dishwasher friendly design makes it easy for parents to clean."

"Aqua stack can be used indoors, in the bath, and outside, in the sandpit of course."

Check out more of Mackisack's work here.