Short answer. Article 518 tells you where to look next: whatever the Civil Code's chapter on waters does not expressly settle is governed instead by the Special Law of Waters of August 3, 1866, and by the Irrigation Law. The Code only fills gaps those two older statutes leave open, so a water-rights question can require checking beyond the Civil Code itself.
What the law says
All matters not expressly determined by the provisions of this Chapter shall be governed by the Special Law of Waters of August 3, 1866, and by the Irrigation Law.
Civil Code, Article 518 — Suppletory Law On Waters. Read the full provision →
A deliberate gap-filler
The Civil Code's chapter on waters covers who owns rainwater, rivers, springs, and water found underground, plus rules on building reservoirs and drawing water for irrigation ditches on one's own land. It was never meant to answer every question on its own, though. Article 518 says so directly: whatever this chapter does not expressly determine is governed by other, older legislation instead.
Two statutes that predate the Code
The Special Law of Waters of 1866 and the Irrigation Law were both already in force when the Civil Code took effect in 1950. Rather than rewrite their detailed rules on water concessions, distribution, and irrigation-system operation, the Code simply absorbed them by reference, leaving their provisions fully intact for whatever situations its own water chapter does not cover. This layering binds anyone asserting a water right, not just courts deciding a dispute; a claimant who ignores the older statutes and relies on the Code alone risks missing a controlling rule.
What this means in practice
If a dispute involves a point the Civil Code's water chapter addresses head-on, such as ownership of rainwater falling on private land, the Code controls. If the dispute instead turns on something more technical, such as how an irrigation concession is granted or administered, the answer more likely sits in the Special Law of Waters or the Irrigation Law, not in the Civil Code articles themselves.
Why the hierarchy matters
Treating the Civil Code as the only source on water questions can lead someone to conclude, wrongly, that a matter is unregulated simply because it is not mentioned in the Code's water articles. Article 518 is a reminder that Philippine water law is spread across more than one statute, and that a full answer sometimes requires checking legislation the Code itself points to rather than displaces.
Related but separate: mining
The very next article, Article 519, applies the same idea to minerals and mineral lands, which are likewise governed by special laws rather than by the Civil Code's ownership rules. Together the two articles show the Code deliberately leaving certain resource-specific fields to dedicated legislation instead of regulating them directly itself, a pattern that repeats again in Article 648 for water servitudes specifically.
Related provisions
- Civil Code, Article 518 — Suppletory Law On Waters
- Civil Code, Article 519 — Mining Governed By Special Laws
- Civil Code, Article 648 — Special Laws Govern Water Servitudes