Clay Pot Refrigeration
I saw this on YouTube: make a clay pot refrigeration container, called a Zeer Pot, with sand and water. It’s a very simple and effective technique that once constructed is good forever with the addition of water.
As well here’s a great case study how this is helping people in Sudan, along with a technical manual and brief. They use a clay lid instead of a damp towel, which makes more sense for long term usage.