From my own experience the bills had less to do with the electricity used or water but much more to do with the lot value and how much is in the Sims inventory and household inventory (the build mode one)
I had a family getting 27k bills and I checked their household inventory which was packed with seeds from a gnome that was in their personal inventory. I think that added up to about 15k worth the seeds. I also forgot to sell their furniture when they moved so it was all in the inventory as well. Once I deleted it the bills were cut in half. The lot itself is worth a lot so I expect the bills to be higher just not as high as they were.
Getting the frugal sim reward will also bring them down. Some eco life items give a bill reduction but I've found it is most often the lot value and how much is in the inventory. My sims returned with treasure from Salvedorea and that week they had high bills because, again, the inventory shot up by 20 grand in the value of the treasure.