> For a total of about 5.75 liters

Wow, to me that seems like a huge amount. Here's what I drink in a typical day:

300ml before breakfast
200ml milk with breakfast
200ml mid-morning coffee
200ml afternoon coffee
200ml evening coffee

A total of 1.1 litres. Occasionally I need another 200ml to top up (eg if I eat something salty, or drink alcohol). Cooking a 100g portion of rice takes me 300ml. Brushing my teeth can be done in 100ml. So 2 litres a day would be ample.

This is in the UK, working a desk job. My room temperature rarely strays outside 21c. Obviously a lot depends on the scenario. If you are actively working outdoors to rebuild society with a chainsaw I can understand needing a lot more. If I am cowering at home waiting for the government to sort it all out, then the above would be about right.

Edit: I guess we all need to measure our own usage rather than relying on other people's. I wouldn't want anyone to use my figures if they really needed 5L plus. On the other hand, I wouldn't want anyone to give up because 12 people x 3 days x 5L was too much to practically store and rotate.