Bizkaia reservoirs fall to 55.6% despite Saturday's downpour

The downpour doesn't halt the deficit: Bizkaia loses 12 hm³ of water in a year

On Saturday, 94.4 litres per square metre fell in Arrigorriaga. On Monday, the reservoirs supplying Bizkaia stood at 55.6% of their capacity, with 121.5 cubic hectometres. A year earlier, on the same date, there were 133.5 hm³. The storm was a patch. The hole remains open and measures 31.9 hm³ below the guarantee curve, the line marking the desirable level to avoid entering a drought scenario.

The report, published by Deia, does not describe a one-off event. It describes a trend: September was the driest of the century in Euskadi. And on that figure a debate has been built that goes far beyond Bizkaia. Because the underlying question is not whether it rained on Saturday. It is what happens when water demand rises every year and the infrastructure that stores it is more or less the same as always.

More taps, the same reservoirs

The Zadorra system holds the bulk of the reserves: 107 hm³, 55.5% of its capacity. The Artiba, Oiola, Nocedal, Zollo and Undurraga reservoirs add up to 2.5 hm³ and stand at 66.4%. Ordunte stores 11.9 hm³, at 54%. They are the same names as decades ago. The population that drinks from them is not.

That is the first point of disagreement. Some argue the problem is arithmetic: if every year there are more people connected to the network, more tourists and more economic activity, the same reservoir capacity falls short. The most pessimistic calculation says the reservoirs were designed for a population far smaller than today's and that the margin has been eaten away without anyone building anything new. Against this stands the opposite argument: the good sites for reservoirs are already in use, and adding more is not always possible or desirable.

What almost nobody disputes is that household consumption is a small part of the total. The bulk goes to agriculture. And there another recurring figure appears: around 30% of irrigation water is wasted through poor practices. If corrected, the savings would be greater than any public awareness campaign.

How much water does a data centre consume?

The arrival of artificial intelligence has introduced a new player into the equation. Data centres cool their servers, and some do it with water. The figure circulating in the conversation is striking: one of these complexes can consume the equivalent of the supply of hundreds of thousands of people. There is no official figure in the material to confirm it, but the concern has taken hold.

The rebuttal comes quickly: not all data centres use water. Some use closed cooling circuits and what they really consume is electricity. The debate therefore shifts from water to energy. And from there, once again, to infrastructure.

The dripping tap in the old pipe

There is a third front that does not make the headlines: network losses. It is pointed out that a large part of the water is lost before reaching the meter, in old pipes that nobody renews. The figure is not quantified, but the image of the hole-riddled cheese keeps coming up. If the communicating vessel leaks along the way, filling the reservoir is of less use.

Added to all this is suspicion about management: that water is turbined to produce electricity at the hours when power is worth most, which alters the reservoir's level. There is no verification in the material, but the hypothesis circulates.

The drought to come

The comparison with the nineties hovers over the conversation. Back then there were restrictions. The question is whether the system would withstand another dry spell with today's population. The answer given by today's figure is not reassuring: 31.9 hm³ below the guarantee curve and a record-dry September.

Saturday's downpour left 81.7 litres in Sondika, 75.3 in Bilbao and 63.1 in Getxo. It served to wet the streets. Not to reverse anything. And that is perhaps the most uncomfortable lesson: the weather can deliver a one-off twist, but the arithmetic of demand and supply is not fixed by a downpour.