Choosing tap water over bottled could save around 0.22 kg CO2 per litre (see here for full calculation and assumptions).
The CO2 values in the slider have been averaged over a month, and split equally over the four data points, calculated as follows:
Q. How regularly do you ask for tap water instead of the tasteless, overpriced and environmentally disastrous bottled stuff?
Endpoints:
Never = 0 kg
Always - (0.22) x (7 days) x (4 weeks)) = 6.16 kg CO2
Midpoints:
A bit - (6.16) x (1/3) = 2.05 kg CO2
A lot - (6.16) x (2/3) = 4.11 kg CO2
