{{lang|cy|'''Hafren Dyfrdwy'''|italics=no}} ({{langnf|cy|Welsh|[[River Severn|Severn]] [[River Dee, Wales|Dee]]}}, after the two main rivers in its region) is a [[water company]] providing [[water services|water]] and [[wastewater treatment]] services, operating in north east and mid Wales. It provides water only in [[Wrexham County Borough|Wrexham]] and parts of [[Denbighshire]] and [[Flintshire]] and both water and wastewater in northern [[Powys]]. It previously served north east Wales and parts of North West England as '''Dee Valley Water''' until June 2018. Its parent entity, Dee Valley Group plc had shares listed on the [[FTSE Fledgling Index]] on the [[London Stock Exchange]], but was purchased by [[Severn Trent]] in February 2017.<ref>{{cite web|url=https://www.deevalleywater.co.uk/wp-content/uploads/2017/02/Press-release-day-one-15-02-17.pdf|publisher=Severn Trent Water|title=Severn Trent and Dee Valley come together to build on strong customer legacy|date=15 February 2017|access-date=28 November 2017|website=deevalleywater.co.uk}}</ref>
The company is regulated under the [[Water Industry Act 1991]].
On 1 July 2018, all of the water service area of Dee Valley Water and Severn Trent lying in Wales became part of the Dee Valley Water company, which was granted a new wastewater appointment and renamed as {{lang|cy|Hafren Dyfrdwy|italics=no}}, ({{langnf|cy|Welsh|Severn Dee}}).<ref>{{Cite web|title=Overview {{!}} About Us {{!}} HD Cymru|url=http://www.hdcymru.co.uk/about-us/overview/|access-date=2021-08-04|website=www.hdcymru.co.uk|language=en}}</ref><ref>{{cite web|url=https://www.ofwat.gov.uk/wp-content/uploads/2017/12/Proposal-to-vary-the-appointments-of-Severn-Trent-Water-and-Dee-Valley-Water-cons.pdf|title=Proposal by the Water Services Regulation Authority (Ofwat) to vary the appointments of Severn Trent Water Limited ("Severn Trent Water") and Dee Valley Water Limited ("Dee Valley Water") as a water and wastewater services company and water only company respectively.|date=8 December 2017|website=[[Ofwat]]}}</ref><ref>{{Cite web|url=https://beta.companieshouse.gov.uk/company/03527628|title = HAFREN DYFRDWY CYFYNGEDIG overview - Find and update company information - GOV.UK}}</ref> The remainder of Dee Valley Water, lying in England (at Chester), was taken over by sister company Severn Trent Water.
