C-MeX and D-MeX development process

The development of C-MeX and D-Mex began in November 2016 when we issued an initial consultation on the future of the service incentive mechanism (SIM).

We presented our initial views on the replacement for SIM, and gave another opportunity for consultation as part of the draft methodology consultation for PR19 in July 2017.  We followed this up with our first set of decisions about C-MeX and D-Mex in the final methodology decision document, published in December 2017.

Dedicated C-MeX and D-MeX development commenced in 2018 with the design and implementation of the pilot phase, and will be followed by the shadow year in 2019, before C-MeX and D-Mex become fully operational in 2020. There have been stakeholder working groups that we have engaged with as part of the pilot phase of C-MeX and D-MeX.

C-MeX and D-MeX pilot

In 2018-19 we completed the pilot of C-MeX and D-MeX, which involved running a series of test surveys in order to inform our decisions.

Pilot timetable

The proposed C-MeX and D-MeX methodologies were tested in the pilot during 2018-19. We appointed consultants to provide advice and make recommendations to us on the two new customer service incentive mechanisms, C-MeX and D-MeX.

  Pilot Wave1 Pilot Wave 2
C-MeX                 Customer Experience survey 8th May – 22nd June 2018 7th August – 23rd October 2018
C-MeX                Customer Service survey 16th May – 11th June 2018 20th September – 22nd October 2018
D-MeX 18th June – 17th July 2018 4th October 2018 – 2nd November 2018


The pilot reports can be found here:

Allto consulting’s C-MeX pilot report

Allto consulting’s D-MeX pilot report

The recommendations and conclusions presented in the pilot reports are those of Allto, based on their experience of running the C-MeX and D-MeX, and do not necessarily reflect the final policies that will come into force in 2020. All policy decisions remain with Ofwat.

Shadow year

Following on from the pilot phase, both C-MeX and D-MeX will be run from May 2019 – March 2020 in shadow form. The shadow surveys will take place throughout 2019/20.

On March 8th we published the following documents in support of the shadow year:

C-MeX policy decision document

D-MeX policy decision document

C-MeX guidance for the shadow year

D-MeX guidance for the shadow year