It shall be the duty of each water undertaker to comply with any arrangements entered into by it under section 87(1) above.
Where, pursuant to any such arrangements, the fluoride content of any water is increased, the increase may be effected only by the addition of one or more of the following compounds of fluorine—
Subject to subsection (4) below, water to which fluoride has been added pursuant to any such arrangements entered into by a water undertaker (with a view to its supply in an area) may be supplied by that or any other undertaker to premises in any other area (whether or not that other area is the subject of arrangements under section 87(1) above).
Subsection (3) above applies if (and only if) the undertaker or undertakers concerned consider that it is necessary for the water to be supplied in the other area—
In this section—
In subsection (4) above, "serious deficiency in supply" means any existing or threatened serious deficiency in the supply of water (whether in quantity or quality) caused by an exceptional lack of rain or by any accident or unforeseen circumstances.
Arrangements entered into under section 87(1) above shall remain in force until the relevant authority, after giving reasonable notice to the water undertaker, terminates them.
But (except where it is reasonably practicable to terminate the arrangements separately), arrangements to which section 87(8)(a) or (b) applied may only be terminated by the relevant authorities acting jointly.