Short answer. You have the right to build a rainwater reservoir on your own land, but it comes with one firm condition. Article 511 of the Civil Code grants landowners this right only provided the reservoir causes no damage to the public or to third persons. The right is real but not absolute.
What the law says
Every owner of a piece of land has the right to construct within his property, reservoirs for rain waters, provided he causes no damage to the public or to third persons.
Civil Code, Article 511 — Right To Build Rain Reservoirs. Read the full provision →
The right to build a rain reservoir
Article 511 of the Civil Code grants a positive right to landowners: Every owner of a piece of land has the right to construct within his property, reservoirs for rain waters, provided he causes no damage to the public or to third persons. You do not need anyone's permission to collect rainwater on your own land by building a reservoir, and no neighbor can object to the mere fact that you are doing so on your property. The article treats this as an ordinary incident of land ownership — the natural right to make productive use of one's land, including capturing water that falls on it.
The no-damage condition
The right is conditioned on causing no damage to the public or to third persons. This limitation is the core constraint. A reservoir that floods a neighbor's land, erodes boundaries, contaminates a shared water source, or creates a hazard to people passing by violates the condition and falls outside the protected right. The size, location, construction method, and management of the reservoir all matter: a reservoir that is safely built and maintained within your boundaries, that does not alter natural water flow patterns in a way that harms others, and that does not create risks for the surrounding community, stays within the right Article 511 grants.
Damage to the public versus damage to third persons
Article 511 covers two categories of potential harm: damage to the public and damage to third persons. Damage to third persons refers to specific, identifiable harm to neighboring landowners or others with identifiable property interests nearby — flooding an adjacent field, blocking a downstream water channel, or destabilizing a neighboring structure. Damage to the public is a broader category — it includes harm to common resources, public infrastructure, or the general community. A reservoir that overwhelms a public drainage system, contaminates a public water source, or creates a public health or safety risk would fall into this category. Both types of harm are prohibited.
What this means practically
If you plan to build a rainwater reservoir on your land, the Civil Code's baseline rule is that you may do so. The responsibility is on you to ensure that the construction and operation of the reservoir does not cause damage to neighbors or to the public. This means thinking carefully about where the reservoir will be located on your property, how runoff and overflow will be managed, how the structure will hold up in heavy rain or floods, and whether any downstream effects of capturing rainwater on your land could affect others. Local government regulations, building rules, and environmental requirements may also apply and should be checked in addition to the Civil Code's baseline rule.