5After a local authority have, under paragraph 2 above, determined what proportion of their estimated expenditure in respect of a particular financial year is to be met out of direct charges, they shall, before such date as may be prescribed in relation to that year, determine such rate or rates of direct charges in respect of that year as will, when calculated in accordance with the provisions of section 49 (payment for water supplied by meter) of the 1980 Act, produce sufficient money to meet the said proportion; and different rates of direct charges may be determined for different circumstances.