We don’t have an approximate number for this, but you should be able to estimate this – you can assume there could be a range of 5-20 people on the site at any time. You could research the global average use of water per day online then use this, or Griffith University did some research in remote communities and found in this The Conversation article: “The data revealed an average daily use of 900 litres per person, rising to more than 4,000L per person per day in some cases. (The average southeast Queensland household daily use is around 180L per person.)” However keep in mind I believe this is household use so quite different to camping on Country where water is sparse, and perhaps rainwater tanks are used.
You will need to make some assumptions about water usage based off figures like this, so check out our FAQs document for guidance on making assumptions like this in your project where more accurate figures aren’t available.
Best of luck with your project,