I would still split the line and install sub-meters but then build some $ amount into the lease to cover the expected usage.

@Donald S. was basically spot on in his estimate for you, the city goes by room not usage and for my 2/1 duplex it's $83 for sewer technically per month (water is quarterly).

If this agreement didn't exist, then this would appear to be an "open and notorious" usage of the driveway.

. $60K with 12 days of personal usage by the owners.  

Usage from the water company shows using 0.2-0.4MCF per month...consistently...for 2 years.

Washer/Dryer in upstairs unit only. 5 star rated home, walls 18" thick.Summer months:Electric between $250-$350/monthFuel between $100-$150/month (60-100 gallons) when turned on, some months we just turn the boiler off (JUN-AUG)Water/Sewer free except septic maintenance. so far this has been $0 total, but I expect to maybe get it pumped just in case late this year (rough guess $300)Winter months:Electric between $350-$450 monthFuel varies greatly with temp, heaviest usage months, I've purchased 300 gallons per month at the extremes of -40 and below temps.Water/Sewer still no monthly actual cost, but I plan on about $25/month to save for annual maint.When I average out my fuel costs simply taking fuel expeditures divided by 12 months, I get approx. $200/month.

There is a sense of urgency for them when they are paying the bill and mysteriously the usage goes down.  

Then you can bill the tenants for some or all of their actual usage, depending on what you are able to split off.If you ARE going to end up paying the utilities, you MUST be vigilant in preventing abuse from the tenants.

I worry that I may try and apply my experience in London to other US cities where it's completely inappropriate!

The water and sewer bill will ALWAYS remain in the Owner’s name therefore the ultimate responsibility of the water and sewer bill will ALWAYS fall onto the Owner.See http://www.clevelandwater.com/customer-service/faq for more info.Holton-Wise does not charge the tenants for water and sewer usage because of all the legal difficulties put in place by Ohio Landlord Tenant Law and the City of Cleveland, Division of Water.