The firm was appointed emergency contractor in May when Daniel fell into administration threatening to disrupt water mains upgrade work in Wales.
Amey will start work on the new contract in October, which is valued at over £18m a year.
It will see Amey take on responsibility for repairing and maintaining around 20,000km of clean water pipes, as well as meter installation and new connections, in an area stretching as far west as Pembrokeshire, north to Ceredigion, east to Herefordshire, and south to Glamorgan
Mel Ewell, Amey’s Chief Executive, said: “The award is testament to the hard work of 300 employees, who joined us earlier in the year when were appointed as an emergency contractor.
“Their continued delivery of high quality services has enabled us to develop our partnership with Welsh Water and we remain focused on providing an excellent service to the public who use their water facilities.”