a couple of hundred litres of fresh water and 80 litres of grey water, 'cos that was the space available.
Grey water disposal depends. Sometimes on the ground, sometimes a dump point. Never near a watercourse.
Black I have two 14 litre cassettes (vacuum loo no longer available new). It really depends on where black will be emptied. Some places its been difficult digging a hole for 14 litres. Other places it would need a very long pipe to reach the public loo. Where there are dump points its different again.
Other answer ...
Normal water use is about 20 litres/day. We can scrimp and use lots less, or use more. For two people black accumulates at 4-5 litres per day, but can be less if male pees on the ground. Grey water probably accumulates at about 5 litres per day.
Not a commonly held view but the cross-section of sink has a large influence on water consumption.
We generally see our constraint as being able to fill with water. There's always somewhere to empty.
Crystal ball gazing ...
there are various attempts at "leave no trace" or "self contained" in various countries. Some of those schemes (including one in Aus) mandate the minimum tank sizes for number of people (or was it vehicle). The Oz schemes are still immature IMHO. My view (or perhaps hope) is that at some way off time in the future Aus State or Federal governments will intervene (they've regulated pretty well everything else). Number of used loo paper festooned bushes in Oz is higher than most countries.
