Section 36. The district commission shall annually determine the amounts required for the payment of principal and interest on such bonds and notes issued or to be issued by the district which will be due during the ensuing calendar year and shall apportion the amounts so determined among the several cities and towns or parts thereof in the district in accordance with the provisions of the plan approved under section thirty-two. The district commission shall also annually determine the amounts necessary to be raised to maintain and operate the district during the said year, for capital outlay items the cost of which is not to be funded, and for all other matters for which the district is required to raise money, and if and to the extent said plan so requires shall apportion among the several cities and towns or parts thereof the amounts so determined in accordance with the provisions of the said plan reduced by the amounts of revenues of funds which are available or are to be received by the district during said year and are applicable to costs of maintenance and operations. Each amount so apportioned for each city or town or portion thereof shall prior to December thirty-first, in each year, be certified by the district commission to the assessors of each city and town included in whole or in part in the district. The assessors of each such city and town shall without further vote include each amount so certified in those amounts to be annually raised by taxes under section twenty-three of chapter fifty-nine; provided, however, that in the event only a part of a town is within the district, the assessors shall assess a tax to the amounts so certified only on the property within such part. The respective city or town treasurers shall pay the amounts so certified to the treasurer of the district in four substantially equal payments, to be made on or before the first day of March, June, September and December.

A city or town in a district may raise all or a portion of the amounts certified annually by the district to the assessors of such cities and towns as provided in the preceding paragraph, through equitable and proportional charges against inhabitants, corporations, and other users for the services rendered by the district in each such city or town. For the purpose of establishing an equitable and proportional schedule or reasonable charges, the property benefited by the services of the district may be classified taking into consideration the volume of water, including surface or drain waters, the character of the sewage or industrial or other wastes, and the nature of the use made of the sewerage system, including the facilities. The charges may include standby charges to property not connected but for which the district's facilities have been made available.

The schedule thus established may be modified in accordance with the plan and as may be necessary to raise the amounts required by the district. The failure of such user charges to raise the amounts required by the district in any year shall not relieve any city or town from its obligation to provide the amounts assessed by the district hereunder.

If a city or town fails to pay the district commission the apportioned amount, the commissioner of corporations and taxation is authorized and directed to pay to the district commission such amounts from the city's or town's share of monies distributed by the commonwealth on an annual basis.