I read here some weeks ago that the installation of a Smart Meter was
not mandatory, but I have just received a notice about the impending
installation of a water meter in Essex.

It includes this note:

"Do I have to have a meter?

Yes, where technically possible. The Secretary of State for the
Environment has approved our plan to meter customers' properties
because we are operating in an area designated as being under severe
water stress."

In this case, as the place is subject to limited occupation, say
about one week per month on average, having metering may well be
advantageous, and I have the option of remaining on the old payment
system for up to two years.

--
Davey.