According to the Spanish Government, the water reserves of mainland territory were at 40.4% of the total capacity of reservoirs and dams on Tuesday, with 22,689 cubic hectometres of water stored, a decrease of 832 cubic hectometres in a period of one week.
A year ago, there were 27,092 cubic hectometres stored and the average for the last ten years is 33,595, according to the same official data.
Storage on Tuesday in the Guadiana river basin, one of which Portugal and Spain share, was at 26.2% of total capacity in Spanish territory, one of the lowest values recorded in the country.
In the Douro and Tejo, other rivers that cross the two countries, water reserves were at 43.7% and 41.5% in Spain, respectively, while in the case of Minho they exceeded 51%.
In the case of the Guadiana, the 2,490 cubic hectometres of stored water is less than half the average of the last ten years (5,256).
In the Douro, there were reserves of 3,278 cubic hectmometres of water on Tuesday, less than the 4,691 of last year and the average of 5,026 in the last ten years.
In the Tagus, storage is at 4,587, compared to 4,916 a year ago and the average for the last decade is 5,986.
The level of Spanish water reserves is the result of "scarce rainfall" across the country, according to the Ministry for Ecological Transition and Demographic Challenge, which publishes this data.
Spain this year is experiencing the worst drought since 1981 and a summer so far marked by "extreme" temperatures and three heat waves, according to the Spanish meteorological agency (Aemet).
The lack of water has led regional governments and municipalities across the country to adopt measures to control consumption, including cutting off the supply during night, consumption limits per person in each house and banning showers on beaches, washing cars, watering the garden and filling private swimming pools.
The situation particularly affects the regions of Galicia, Andalusia and Catalonia, but there are measures to cut water consumption to be adopted throughout the country.
In the case of Andalusia, the dams and river basins are already below the necessary capacity to supply the population in the coming months, according to regional authorities.