Viseu Agrees a 40-Year Water Deal to Replace the Ageing Fagilde Dam, but Its Municipal Assembly Must Still Approve It

Viseu City Council has signed an agreement with Águas do Douro e Paiva, the state-owned company that supplies bulk water to the south of Greater Porto. Under it, the company would build a larger dam at Fagilde and a new water treatment plant, and link Viseu's supply to the Douro river. SIC Notícias reported the signing on Friday. The deal runs for 40 years and foresees almost 200 million euros of investment in the bulk water network, but it is not final yet: Viseu's Municipal Assembly still has to approve it.

That vote matters well beyond the city. Viseu and four neighbouring councils draw their water from a single reservoir behind a dam that is more than 40 years old.

Why Fagilde matters

The Fagilde dam, on the Dão river, was finished in 1984. When the government announced its replacement in July 2025, it said the structure had "serious structural anomalies", including internal sulphate reactions in the concrete and limited safety outlets. Water has gone over the top of it twice, in 1995 and 2000,. The reservoir holds 3.84 cubic hectometres. The new dam, about 100 metres downstream, would double that to 7.68, at an estimated cost of 35 million euros with EU co-funding from the Sustentável 2030 programme, and the government set a completion date of the end of 2029.

"The new Fagilde dam is the concrete answer to decades of structural risks, supply failures and stopgap solutions," the Environment Minister, Maria da Graça Carvalho, said at the time.

The supply failures are not theoretical. In the autumn of 2017, SIC recalls, the reservoir ran so low that more than 100 lorries were mobilised to keep drinking water reaching Viseu, Nelas, Mangualde, Sátão and Penalva do Castelo.

A deal against a deadline

The legal route is Decreto-Lei 82/2025 (Decree-Law 82/2025) of June 2025. It extended Águas do Douro e Paiva's southern Greater Porto system inland and placed the Fagilde dam itself inside the company's concession. It also gave nine councils (Mangualde, Nelas, Oliveira de Frades, Penalva do Castelo, São Pedro do Sul, Sátão, Vale de Cambra, Viseu and Vouzela) the right to join, each by a vote of its municipal assembly.

The original window was one year. In August, Decreto-Lei 159/2026 stretched it to 16 months from the 2025 decree's entry into force, because councils needed longer "to weigh the technical, financial and strategic implications". Observador, reporting the extension via Lusa, said the new deadline ends in October.

The road to this week has been political. Viseu's assembly voted to join the system in June 2025 under the then mayor, Fernando Ruas (PSD). His Socialist successor, João Azevedo, reopened the terms after last year's local elections, insisting in August that "the new Fagilde dam has to be part of this process" and that building it was "an obligation of the Portuguese state". According to SIC, the agreement now signed includes it.

What is still unknown

Neither the council nor the company has yet published the agreement, so several points rest on SIC's report alone. It is not clear how the almost 200 million euros is split, whether it includes the 35 million euro dam, who pays for the treatment plant, what Viseu receives for handing over its bulk water infrastructure, or whether the other councils will follow Viseu before the deadline. The 2025 decree said joining would not change the company's existing tariff, because its concession is extended by ten years. What Viseu households will pay is not yet public.

Water security inland has been a recurring theme this year; see our report on the Caldeirão dam and the Mondego in August.

Sources: SIC Notícias, 2 October 2026; Portuguese Government, 15 July 2025; Decreto-Lei 82/2025 and Decreto-Lei 159/2026, Diário da República; Lusa via Observador, 20 August 2026 (all in Portuguese).

Feature image: the Fagilde reservoir. Photo by Vitor Oliveira (CC BY-SA 2.0), via Wikimedia Commons.