Almost a billion people do not have access to clean and safe water. Access to safe drinking water and sanitation is increasingly being considered a fundamental human right. Corporations play an important role in the realization of the right to water. For example, they can become violators of the right to water where their activities deny access to clean and safe water or where water prices increase without warning. Corporations can have a positive or negative impact on the human rights of individuals, wider communities and indigenous peoples. This paper argues that corporations bear a certain responsibility for the realization of the human right to water, which can be derived from international as well as national (constitutional) law. Corporate obligations under the human right to water can potentially be based on the right to water as set in national law and in the international human rights treaties and in corporate codes of conduct. It is asserted that this responsibility is different and separate from the responsibility of state governments and should never undermine state obligations to observe the human right to water. In short, the paper argues that corporations have an obligation to respect, protect and fulfil the right to water deriving primarily from national legal orders.