Document Type

Symposia Article


Although rainwater harvesting would appear to be a win-win solution to the problem of developing new sources of water, implementing rainwater harvesting in the American West has been fraught with tensions that have pitted rural farmers and other agricultural interests against urban and suburban homeowners. The water law of the western states is based on the prior appropriation doctrine, which creates a “first in time, first in right” system of water rights tied to when a user diverts surface water for beneficial use. Since water rights are property rights, state statutes and regulations that “go too far” in affecting them risk giving senior appropriators a takings claim. Based on the nature of rainwater harvesting and judicial interpretations of federal and state constitutional takings clauses, the most likely claims by downstream agricultural irrigators in the West are that state statutes authorizing rainwater harvesting are per se physical takings. Such takings require compensation, even though they do not result in the total loss of the right to use water or have a minimal economic impact on a senior appropriator. To avoid a taking, state legislatures need to draft these statutes in ways that take advantage of how existing state laws implement the prior appropriation doctrine. Colorado’s most recent rainwater harvesting statute leverages how the no-injury requirement placed on junior appropriators ultimately limits the scope of the senior appropriators’ water rights and avoids a taking.

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