The rainfall

Average precipitation in Guanajuato runs around 650 millimetres a year. The figure alone says little, because the average conceals two variations that do matter: where it falls and when.

Where it falls

The state is not homogeneous. The Bajío plain in the south is the wettest part, on the order of 700 millimetres a year. The north of the state receives considerably less — around 500 millimetres, and in parts of Ocampo and San Felipe the records fall to figures near 380.

That gradient is why agriculture and industry sit where they do. The south has the alluvial soil and the rain; the north has the sierra and the dryness. The industrial corridor follows the wet band, not by design but because it followed agriculture, which did choose it.

When it falls

Bajío rainfall is intensely seasonal. It concentrates between June and September, with July the wettest month — on the order of 170 millimetres. February and December record under ten millimetres.

Put another way: four months of rain and eight months dry. Which means water availability does not depend on whether it rains, but on storage capacity and on how fast the aquifer recharges. A plant that consumes water year-round is supplied, in practice, from what was left underground.

The mismatch between recharge and extraction

Here is the structural problem, and it is a problem of rates.

An aquifer recharges by infiltration, a process that can take years or decades. A pump extracts in hours. As long as annual extraction exceeds annual recharge, the balance is negative and the water level falls, year after year, regardless of how good the rainy season was.

In Guanajuato that balance has been negative for a long time. Nineteen of the state's twenty aquifers are in deficit; only Xichú–Atarjea is in balance, and eighteen are classified as overexploited. Roughly 80% of the volume goes to agriculture.

The consequences are not only about volume. An overexploited aquifer can show water-quality deterioration, well drawdown, and differential land subsidence — the last with direct effects on slabs, foundations and industrial buildings.

What changed in concessions

Until recently, buying a parcel with a well usually meant inheriting the associated concession title. That assumption is no longer safe: free transfer of concessions between private parties has stopped operating as it did, so the physical existence of a well does not amount to a transferable extraction right.

The practical consequence is that water due diligence has stopped being a formality and become a condition of viability. A parcel with a well, no valid title and no transfer route, is a parcel without water.

What to verify

• Existence and validity of the concession title in REPDA, in whose name and for what volume
• Annual concessioned volume against the real consumption the process requires, including operation at full capacity
• Aquifer status and whether the current availability publication admits new allocations
• Transfer route for the title under the current regime, if one exists at all
• Discharge permit and real capacity of the treatment plant that will receive the effluent

None of these five questions is answered by walking the parcel. All of them are answered with a file.