Hi @Charles43, as far as I'm aware, Airbnb does not have the option to charge an extra fee for utilities such as gas/water/electricity etc. This should be built into your nightly rate. If you expect guests to be able to budget for their trip, you should present them with the final booking cost upfront. I doubt many people will appreciate the inconvenience of added extras that need to be paid at a later date.
Are you trying to get them to conserve? I've never heard of charging for electricity and water. I would charge more and detail the need for conservation in your house rules.