This is one of the common questions I solve with my trainees.
You can do the following:
- Think about the total number of liters consumed by one person per day (say 2L)
- You need to think about your consumption habits during one week (one day would be too short as it doesn't represent all of your habits, or one month would be too long as you won't remember all of your habits)
- Thus, break your consumption occasions into "at home", and "away from home" (this would include e.g. restaurants, at work, at gym etc.)
- For each consumption occasion, assign a % of your water consumption (and thus in total, it should sum up to say, 2L/day)
- To recap, you should have something as follows (as an example):
- At home: 1L/day
- Away from home (at work): 0.5L/day
- Away from home (restaurants): 0.2L/day
- Away from home (at gym): 0.3L/day
- The next step is that you need to say that you represent an average consumer and thus you can extrapolate your consumptions to the whole population
- For each consumption occasion, you can also segment into tap water/filtered water vs. bottled water dependent on the type of the question
Hope the approach was clear, sorry for the long explanation.