Australia's Millennium drought, a 13-year dry period unprecedented in the instrumental record, inspired a change in the extant water management principles. The Water Act of 2007 was introduced and required the preparation of a Basin Plan to set environmentally sustainable levels of water extraction and to reduce the over-allocation of water entitlements that threatened water security. The Act was unusual in that environmental considerations were initially interpreted as a non-negotiable constraint on other water uses because of the legislative context in which it was written. This framing shaped subsequent negotiations during development of the Basin Plan. The recent passing of this Plan into law provides a conclusion to this complex, messy and, at times, irrational reform process. The path taken, from genesis of the Act to its eventual culmination in the Basin Plan, provides internationally important lessons in legislating for sustainable water management in inter-jurisdictional river basins. However, the reforms have also created new opportunities for ongoing improvement, including the mutual benefits derived from managing environmental water and irrigation water cooperatively.