Every utility shall offer residential customers a voluntary budget billing or levelized payment plan for the payment of charges. The plan shall be designed to reduce fluctuations in customers' bills due to seasonal patterns of consumption. Any such plan shall also be offered to customers who are condominium associations or cooperative housing corporations.

Unless otherwise authorized by the commission, each such plan shall be based on the customer's recent 12-month experience, adjusted for known changes. If 12 months of billing data are not available for the customer then 12 months of billing data for the premises shall be used. If 12 months of billing data are not available for the premises then the utility shall estimate future consumption over the next 12-month period. Each such plan shall provide that bills clearly identify consumption and state the amounts that would be due without levelized or budget billing; such information need not be supplied on interim bills for customers billed on a bimonthly basis. Each such plan shall provide that bills be subject to regular review for conformity with actual billings.

Each such plan shall be filed with the commission and any significant changes in the plan shall be submitted to the commission for review before implementation.