(g) A landlord shall determine a calculated cost per unit of water consumption by dividing the total amount of any bill or invoice provided to the landlord from the water company for water usage, the customer service charge and taxes, but not including any interest for the late payment, penalty fees or other discretionary assessments or charges, for all water provided to the premises through the water company meter in that billing period, by the total amount of water consumption for the entire premises. The total amount charged separately to each submetered dwelling unit for water usage for any billing period shall not exceed such calculated cost per unit of water multiplied by the number of units of water delivered exclusively to the particular dwelling unit for the same billing period, provided that the landlord has verified that the total amounts of water usage measured by all submeters in the building, including all submeters for common areas, does not exceed the total amount of water usage in the building for the same billing period as shown on such bill or invoice.
(h) Whenever a tenancy in a dwelling unit commences after the beginning, but before the end, of a billing period for which the landlord has not been billed by the water company, the landlord shall mail to the tenant on the first day of such tenancy the reading on the submeter for the dwelling unit as of that day. The landlord may thereafter bill the tenant only for the water measured on the submeter subsequent to such reading.