Law
The Public Trust Doctrine Applied to Groundwater
Quick fact
In 2021, the Hawaii Supreme Court ruled that the public trust doctrine applies to all groundwater, making the state a trustee obligated to protect it for public uses, even when private wells are involved.
Why this is interesting
You own the land above an aquifer—so you own the water below it, right? In some jurisdictions, that assumption is being overturned by a doctrine nearly two thousand years old.
Read the full explanation
Understanding The Public Trust Doctrine Applied to Groundwater
The public trust doctrine is a legal principle that certain natural resources—originally limited to navigable waters and shorelines—are held by the state for public use and cannot be privately owned or alienated. For centuries, it meant that a state must protect the public's right to fish, swim, and navigate in waterways. Groundwater, on the other hand, was traditionally treated as a private resource: whoever pumped it from beneath their land could claim it, subject only to simple rules like 'reasonable use.' The idea that the public trust could extend to groundwater is relatively new. It emerges from recognizing that groundwater and surface water are hydrologically connected, and that the public's interest in aquifers—as drinking water, for ecosystem support, and for future generations—is just as real as its interest in lakes and rivers. When a court applies the doctrine to groundwater, it means the state has an affirmative duty to consider public uses and cannot prioritize private extraction over the health of the entire water system. This shifts the debate from 'who owns the water?' to 'what does the public need?'
A deeper explanation
The mechanism of this extension lies in the evolving interpretation of the state's role as trustee. Under the classic doctrine, the state holds title to navigable waters and submerged lands for the public. The modern application to groundwater hinges on the physical reality of the hydrologic cycle: groundwater discharges into surface waters, and surface waters recharge aquifers; they are one interconnected resource. Courts have reasoned that if the public trust protects the shared resource of surface water, it must logically protect the groundwater that feeds it. Legally, this works by establishing that the state's sovereign authority over water resources is broader than mere ownership of beds and banks. Judges have held that the public trust is a 'structural' principle of constitutional magnitude, limiting even the legislature's power to grant away water rights without considering public interests. In Hawaii, for example, the Supreme Court ruled that the state must balance public trust purposes—such as Native Hawaiian traditional practices, domestic use, and ecosystem protection—against private commercial uses. This creates a duty to protect, maintain, and even restore water resources, and it authorizes courts to review and potentially invalidate permits that degrade the resource. The doctrine does not automatically ban private pumping, but it imposes a presumption that decisions prioritize the public interest and that any private harm to the resource must be minimized. This is a fundamental shift from prior appropriation, which favors senior private rights, because the trust is dynamic: it requires ongoing monitoring and adaptation of water allocations as conditions change.