Short answer. It depends on how you acquired the right. If you hold an administrative concession, your rights and obligations are fixed by the terms of the concession document itself; only a right acquired by ten-year prescription is instead defined by how the water has actually been used.
What the law says
The extent of the rights and obligations of the use shall be that established, in the first case, by the terms of the concession, and, in the second case, by the manner and form in which the waters have been used.
Civil Code, Article 504 — Acquiring Use Of Public Waters. Read the full provision →
Two different ways to acquire the right
Article 504 recognizes only two ways of acquiring the use of public waters: by administrative concession, or by prescription for ten years. These are not interchangeable paths to the same kind of right — the article treats them as genuinely different sources, and it matters which one actually applies to your situation, because each one is measured against a different yardstick when it comes to defining what the right actually covers.
If your right came from a concession, the document controls
Where the use was acquired by administrative concession, Article 504 is direct: the extent of your rights and obligations is that established by the terms of the concession. In other words, the written grant is the measure. If you hold a concession, how you have actually used the water since then does not expand or redefine what the concession itself says — the document is what fixes the scope of the right, not your subsequent practice.
If your right came from prescription, actual use controls
The second situation Article 504 addresses is different in kind: a right acquired by prescription for ten years has no governing document to look to in the first place. For that kind of right, the article says the extent of the rights and obligations is defined instead by the manner and form in which the waters have been used. Here, actual, sustained use over the prescriptive period is not just evidence of the right — it is what defines its scope.
Why the distinction matters for you
To answer the question directly: it is not one rule for everyone. If your access to the water rests on an administrative concession, look to that document's terms, because that is what Article 504 makes controlling, regardless of how your actual use may have evolved. If, instead, your claim rests on ten years of use without any such concession, then it is the pattern of that actual use — how, and in what form, the water has been used — that defines what you are entitled to under this article.