Somebody has been winding you up. However, do remember that your hot water tank has about 8 litres in it and the aquaroll will hold 40 litres. More than enough for a good shower, but if you have a large family, or SWMBO wants to do an extensive hair wash, then you will be filling up, and emptying waste a lot. Even a mains connection only feeds cold water, you still have to heat it.
If you want to really splash then use the iste showers, and wait for someone to bang oon the door to tell you to hurry up.