Short answer. Not necessarily. Article 510 provides that owning the land where water rises does not override rights the owners of lower estates have already legally acquired to use that water. If your neighbor validly acquired a right to the flow, your ownership of the spring does not let you cut it off.
What the law says
The ownership which the proprietor of a piece of land has over the waters rising thereon does not prejudice the rights which the owners of lower estates may have legally acquired to the use thereof.
Civil Code, Article 510 — Rights Of Lower Estates Preserved. Read the full provision →
Owning the source does not mean unlimited control
It is true that the owner of land where a spring rises generally owns the waters produced there. But Article 510 makes clear that this ownership is not absolute against everyone downstream. The article states plainly that this ownership "does not prejudice the rights which the owners of lower estates may have legally acquired to the use thereof." In other words, your ownership of the spring coexists with whatever legitimate rights your neighbor already holds over the water that flows down to their land.
What counts as a legally acquired right
The key phrase is "legally acquired." A neighbor's long habit of drawing water does not by itself create a protected right — the use has to have been acquired through a recognized legal basis, such as a title, a contract, an easement properly constituted, or another mode the law recognizes for establishing rights over water. If your neighbor's use rests on nothing more than convenience or your past tolerance, without any such legal basis, Article 510 would not stand in your way of changing how you use the spring.
If the right does exist, you cannot unilaterally cut it
Where the lower estate's right to the water has actually been legally acquired, the spring owner cannot simply divert, dam, or shut off the flow to defeat it. Doing so would violate the very protection the article grants. This does not mean you lose all ability to manage or use the spring water yourself — it means your use must accommodate the portion of the flow your neighbor is legally entitled to, rather than eliminating that entitlement outright.
Why this matters before you act
Disputes like this often turn on facts that are not obvious at first glance — how long the use has continued, what document or arrangement (if any) established it, and whether it was ever formally registered or annotated. Before making any changes that would reduce or stop the flow to a neighboring property, it is worth establishing clearly whether that neighbor's use rests on a legally acquired right under this article, since acting first and sorting out the legal basis later can expose you to a claim for restoration or damages.