With RUBS, a price based on actual use is not sent to the tenant as with
submetering, and the amount of water saved by these systems is unclear, but
ususally there is some percentage of savings.  A hot water hybrid (HWH) billing
system is a combination of submetering and allocation where hot water is submetered
and a formula is applied to estimate the resident's total water use based on the
volume of hot water metered.  HWH systems provide more of a price signal than
RUBS but less than that for sub-metering.  Many multi-family properties around the
country are implementing RUBS programs with great success.  This eliminates the
need for costly sub-metering installation and makes the billing process simpler.  
Normally, the total property water bill is used for the calculation.  The total bill is
reduced by 10% - 25%, for common area usage, and the remainder is divided among
the residents.  Larger units may pay more than smaller units or units with more
occupants may pay a larger percentage in an effort to be as fair as possible.  A
RUBS system is sometimes implemented until a metering system can be installed,
thus helping the owner with water cost expense in the interim.
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A ratio utility billing system (RUBS) or an allocation formula that divides a property's water bill among its
residents based on a ratio of floor space, number of occupants, or some other quantitative measure.

Why Use A RUBS System For Billing?