6. For the purposes of section 1 of the 1968 Act, in determining what is a reasonable cost to take public sewers to such point or points as will enable the owner of premises (or a part of them), which consists only of one or more dwellings and which is to be served by the public sewers, to connect the owner’s drains or private sewers (at a reasonable cost), the cost of taking the public sewers to the point or points is a reasonable cost only if the cost to Scottish Water does not exceed the amount determined by the formula—
where—
“Cs” is the figure which is the average of—
the current charge (fixed as an annual charge) for or in connection with the provision of sewerage to, or the disposal of sewage from, an unmetered dwelling in band B; and
the current charge (fixed as an annual change) for or in connection with the provision of sewerage to, or the disposal of sewage from, an unmetered dwelling in band C; and
“Ns” is the number of dwellings in the premises (or, as the case may be, the part of them) served by the drains or private sewers (of the owner) which are to be connected to the public sewers at the point or points in question.