Winston

That's definitely not right. We are 3 adults in our house, we shower once a day every, between 8 to 12 minutes per shower, plus our kitchen basin, add another 6 minutes per day for the kitchen, so that approximately 30 to 35 minutes per day. Our 9 kg (nine kg), lasts 3 weeks on average. 

At the 7min per day you should have used about 12kg. Thus you used 60% more than calculated. One of the earlier posts indicating only 20g per hour is way out. For a 16-20l/min it should be around 48g/min so 20g/h is just too low. Not even a small gas cooker can use so little gas on a small flame. 
Statements based on manufacturer figures. 
@slipx thanks for your great graph. 

We have a 20L/min Paloma gas geyser that is connected in series to our electric geyser. It only turns on if the temp of the incoming water (output from electric geyser) is below 55 degrees. I run the electric geyser during the day if there is sufficient solar otherwise it stays off. We have roughly 2 baths and 1 shower a day plus the stove and oven run off gas and are used daily. This is how long a 48kg cylinder lasts.