Paying for electricity in Germany

I have seen mention on this forum of paying for electricity in Germany so pass on our recent experience. On an ACSI site in Saarburg we were informed that the inclusive cost was for 4 kw-hrs. We had the Alde on 1 kw  for hot water and, still on first setting, we put the heating on for 30 mins. We are very frugal! Next morning on check-out  the proprietor came to the pitch to check the settings and we had used 5 units. On this occasion she did not charge us but I was astonished that we had used that much power for kettle, hot water and very brief heating.