5.—(1) In article 6, in relation to each class of hereditaments—
(a)in any formula—
y is the relevant amount of water in relation to the period of 3 years ending immediately before the relevant preceding year;
Y, subject to article 6(3), is the relevant amount of water in relation to the period of 3 years ending on 31st March 1999;
Z is a number having the same value as y in the last foregoing year in relation to which the applicable recalculation factor for that class was determined in accordance with article 6(2); and
T has the same meaning as in the definition of “the standard formula” in article 2; and
(b)“relevant amount of water” in relation to a relevant designated person and any period of 3 years means the annual average, over 3 years, expressed in megalitres to the nearest tenth part, calculated in accordance with the formula set out in paragraphs (2) and (3).
(2) The formula referred to in paragraph (1)(b) is
A - B
where—
A is the estimated annual average amount of water put into supply by that person in the period of 3 years, being water supplied—
to any other person in bulk, that is to say for the purposes of augmenting or constituting the supply to be given by that person; or
otherwise,
less half the estimated annual average amount of non-potable water so supplied otherwise than in bulk; and
B is half the annual average amount of water estimated to have been taken or supplied in bulk during that period of 3 years.
(3) Where the relevant designated person did not supply water throughout any year in a period of 3 years, paragraphs (1) and (2) shall apply as if for the reference to the annual average over 3 years there were substituted a reference to the annual average over the number of years throughout which water was supplied; and for the purposes of this paragraph any temporary suspension of supply shall be disregarded.