Traditionally in North of Portugal, in undifferentiated hydrogeological formations, groundwater has been the main source of small populations. The main sources are natural springs and galleries that intercept fractures in hard rock mountains.
The subterranean drainage is driven by a fracture network that can be continuous and not largely conditioned by water courses. The recharge occurs through the precipitation that fall directly into the outcropping layers with well-developed and significant fracturing.
The year 2017 in Portugal was particularly dry. While some cities like Viseu were at risk of running out of water, others like São Pedro do Sul located in same district never lacked water. Why? Because while the former depended on a single source of water, the Fagilde Dam, which was exhausted, the latter was always provided with water supplied by the hundreds of mines located on the slopes of the mountains. Underlying this situation is the fact that groundwater is a much more resilient resource than surface water and therefore more resistant to prolonged drought periods
Currently, due to the fast technological progress – but not always beneficial to people's lives - many galleries, were abandoned although since the oldest times, the populations have been supplied with water captured in several galleries evenly distributed in the mountains, which never failed. This article describes the use of an ancestral groundwater supply system in small parish of São Pedro do Sul as a paradigmatic example of a sustainable use of a natural resource.
Consequently, instead of building more dams that cause large economic, social and environmental impacts with high costs for the population, we must consider the use of much less demanding Natural Bases Solutions such as the ancestral systems described here, which proven to be efficient for centuries.