Residents in the US state of Colorado will vote tomorrow on whether to legalise sports betting, with the aim of conserving water.

Proposition DD, which has bipartisan support, has been referred to the ballot, with voters being asked to authorise US$29m in new taxes per year.

It would allow for sports betting, both in-person and online, starting in May. Colorado would thus become the 20th state with legal sports betting.

Analysts are predicting annual revenues of between $6m and $15m in the first three years and the money would be used to assist in state water conservation plans.