It comes as a series of dramatic images showing the extent of the crisis gripping the Tagus river emerged.
Known as the Tajo in Spain and Tejo in Portugal, the river rises in Aragon, northern Spain passing close to Madrid before forming a length of the border with Portugal and eventually emptying into the sea at Lisbon.
Along its 1,000 kilometre length it is dammed 51 times, but its current problems arise at the headwaters.
And they are likely to exert a knock-on effect in expatriate strongholds on the Mediterranean slope.
Constructed between 1966 and 1979, the 292-kilometre Tagus-Segura transfer is a concrete canal designed to carry water from the upper Tagus to the Segura river basin, where it is used to irrigate crops in Alicante, Murcia and Almeria.
But much of the channel is open to the air, meaning tens of thousands of litres of water are lost to evaporation before reaching their destination.
Environmental organisation Greenpeace this week published a scathing report on water management in Spain, as the country continues to battle its worst drought for two decades.
The study, entitled Drought, Something More Than a Lack of Rain, concludes that 75 per cent of Spain is at risk of becoming a desert and claims that “the problem is not drought, but robbery.”
According to the report, the national government “has not worked to mitigate dry periods” and Spain has instead “lived and legislated as if it were a water-rich country.”
The Entrepeñas reservoir in Guadalajara near Madrid is one of the sources of the Tajo-Segura transfer, but currently sits below 10 per cent of capacity, with local villages forced to ship drinking water in by lorry.