C-MeX and D-MeX 2024-25 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.

The financial payments associated with C-MeX and D-MeX will be detailed in the companies in-period draft determinations and these outperformance and underperformance payments will be confirmed at the final determination stage of the in-period process.

Customer Measure of Experience (C-MeX) 2024-25 results

Rank  Company  C-MeX score  Payment (£m) 
1 Northumbrian Water 80.37 3.175
2 Wessex Water 79.71 1.742
3 Dŵr Cymru 79.56 2.030
4 Portsmouth Water 77.78 0.137
5 Bristol Water 77.76 0.306
6 Hafren Dyfrdwy 77.61 0.073
7 Anglian Water 77.38 2.095
8 United Utilities 76.36 1.829
9 South Staffs Water 74.74 0.000
10 Yorkshire Water 74.48 -0.140
11 Severn Trent Water 74.43 -0.256
12 South East Water 71.82 -0.389
13 Affinity Water 70.10 -0.939
14 SES Water 69.72 -0.202
15 South West Water 69.48 -1.088
16 Southern Water 65.13 -3.407
17 Thames Water 61.44 -13.705

Developer Services Measure of Experience (D-MeX) 2024-25 results

Rank  Company  D-MeX score  Payment (£m) 
1 Portsmouth Water 92.45 0.155
2 Severn Trent Water 92.16 2.574
3 Northumbrian Water 91.91 0.692
4 United Utilities 91.51 0.847
5 Hafren Dyfrdwy 90.84 0.015
6 South West Water 90.43 0.210
7 Wessex Water 90.00 0.102
8 Anglian Water 89.68 0.052
9 Bristol Water 89.63 0.000
10 Affinity Water 89.50 -0.020
11 South Staffs Water 88.03 -0.139
12 SES Water 87.20 -0.066
13 Dŵr Cymru 86.97 -0.886
14 Southern Water 83.75 -1.869
15 South East Water 83.56 -0.663
16 Yorkshire Water 82.06 -1.922
17 Thames Water 79.88 -6.365

BMG report: C-MeX and D-MeX 2024-25 – OFWAT

C-MeX model

D-MeX model

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 that 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; and
  • 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.