C-MeX and D-MeX - 2020-21 results

Residential customers in England and Wales cannot choose their water and wastewater company. Developers and other third parties must also receive certain services from one of the 17 largest water only and water and wastewater companies we regulate.

We encourage the 17 companies providing these monopoly services to deliver better services by (among other things) using incentives. This includes:

  • the Customer Measure of Experience (C-MeX), which measures the quality of services delivered to household customers
  • the Developer Services Measure of Experience (D-MeX), which measures the quality of services to developers and other third parties

Each company is ranked for C-MeX and D-MeX and receive:

  • a positive financial payment if they do better than expected (‘outperformance’)
  • a negative financial payment if they do worse (‘underperformance’).

Performance commitments are the pledges companies made to their customers and stakeholders at the 2019 price review (PR19) about service levels to make progress towards their outcomes. Where a company outperforms against its performance commitments, it sees relevant increases in the amount of revenue it can recover in its price controls. Where a company underperforms against its performance commitments, this reduces the amount of revenue companies can recover from customers.

This is the first year of that companies will receive financial payments and these have been detailed in the companies in period draft determinations. These outperformance and underperformance payments will be confirmed as final at final determination stage of the in period process.

Customer Measure of Experience (C-MeX) 2020-21 results

Rank Company C-Mex score Payment (£m)
1 Portsmouth Water 86.22 0.283
2 Wessex Water 86.09 2.022
3 Northumbrian Water 85.76 2.927
4 Welsh Water 85.15 2.014
5 United Utilities 83.59 2.076
6 Bristol Water 83.31 0.162
7 Anglian Water 83.05 1.127
8 Yorkshire Water 82.78 0.466
9 Severn Trent Water 82.35 0
10 South Staffs Water 81.89 -0.080
11 Hafren Dyfrdwy 81.38 -0.035
12 South West Water 80.96 -0.536
13 South East Water 80.70 -0.401
14 SES Water 78.97 -0.226
15 Affinity Water 77.88 -1.545
16 Southern Water 74.64 -4.906
17 Thames Water 72.92 -16.753



Developer Services Measure of Experience (D-MeX) 2020-21 results


Rank Company D-Mex score Payment (£m)
1 Severn Trent Water 89.70 3.881
2 Wessex Water 89.47 0.698
3 Portsmouth Water 89.20 0.099
4 Hafren Dyfrdwy 89.01 0.035
5 United Utilities 88.44 1.053
6 Anglian Water 87.72 1.175
7 Northumbrian Water 86.94 0.354
8 Bristol Water 86.81 0.055
9 South West Water 85.88 0
10 Affinity Water 84.39 -0.094
11 South Staffs Water 83.59 -0.073
12 Dŵr Cymru 82.69 -0.354
13 South East Water 79.85 -0.239
14 Thames Water 77.56 -1.861
15 Southern Water 73.77 -1.033
16 Yorkshire Water 62.25 -2.884
17 SES Water 60.20 -0.344


Supporting documents

Accent report: C-MeX and D-MeX 2020-21

C-MeX model 2020-21

D-MeX model 2020-21


CMeX DMeX infographic explanation - C-MeX is the customer measure of experience. It looks at residential customers' satisfaction with their water company. D-MeX is the developer measure of experience. It looks at the experience for developer services customers, such as property developers requesting a new connection.

About C-MeX and D-MeX

Following the shadow year of 2019-20 where we piloted the mechanisms, we have now completed the first year of surveying for C-MeX and D-MeX reporting. While financial incentives did not apply to C-MeX or D-MeX during the shadow year, they now do and these have been detailed in the Companies in period draft determinations. We have not made direct comparisons to the shadow year due to some methodological differences, however this now gives us the benchmark that we will be comparing performance against looking forward.

We publish league tables each year which show how each company has performed during the year and an annual report produced by our survey agent Accent.

Now with both incentives in effect since 1 April 2020, companies are incurring significant underperformance payments or outperformance payments based on how they score relative to each other every year – with the largest return of £17.9m a year (C-MeX) to its customers for poor performance. This demonstrates that C-MeX and D-MeX encourages companies to strive to improve customer experiences while also measuring performance across companies consistently, reliably and fairly.

How C-MeX is measured

C-MeX is based on two surveys conducted each month with residential customers:

  • the customer service survey (CSS) – based on interviews with a random sample of customers that have recently contacted their company, using a mixture of telephone and online surveys; and
  • the customer experience survey (CES) – based on interviews with a random sample of members of the public, using a mixture of telephone and face-to-face surveys.

How D-MeX is measured

D-MeX has two components which measure the service provided by water companies to their developer services customers (which include large and small property developers, self-lay providers, new appointees and other customers requesting a new connection):

  • a qualitative component – based on monthly interviews with developer services customers that have transacted with a water company in the previous month
  • a quantitative component – based on the water company’s performance against a key set of Water UK metrics which measure the service provided by water companies to their developer services customers.

* Following the introduction of new self-lay water metrics by Water UK, in February 2021 we consulted on changing the metrics for self-lay providers in D-MeX. In March 2021, we published our assessment and final decisions.

We also consulted on changing the metrics relating to the services provided to NAVs and the adoption of sewerage assets, providing an opportunity for stakeholders to comment in July 2020 and September 2020 we published our assessment and final decisions


Page updated 22 November 2021