You don’t need a refrigerator to keep food cold. All you need is two pots of clay, sand and water, and you have a portable mini-fridge with a time-tested design, writes getpocket.com. After all, people were storing food thousands of years before the refrigerator, right?

“It’s just amazing,” says Paul Smith Lomas, CEO of Practical Action, a British charity that helps people in Latin America, Africa and South Asia find solutions to everyday problems, including food preservation. “We love finding brilliant ideas that can help people solve their own problems.”

Here’s how to make a portable mini fridge:

Take two clay pots – one larger and one smaller, which will fit in the first one. Collect sand and water. Fill the bottom of a large pot with several inches of sand. Place the smaller pot in the larger one and fill the space between the pots with sand. Pour water over the sand. Cover the dishes with a ceramic lid or a damp cloth.

Finished. Now you can store food inside. Remember to add water to the sand every day as the dishes use evaporation to cool the food. As the water evaporates through the clay, it cools the space inside the pot. It’s like splashing water on your face on a hot day; the water evaporates from the skin, cooling it in the process.