Some workplaces have not even thought about how to approach alcohol in work situations, some are banning it altogether, and others are taking more of a middle-ground approach.
The Health and Safety at Work Act and regulations do not specifically cover alcohol and there are no specific WorkSafe guidelines. Nevertheless, the consumption of alcohol in work situations represents a risk which the employer is responsible for managing. Alcohol poses potential for serious harm, for example, if workers become intoxicated and then drive under the influence.
Even though an employer is generally not responsible for an employee once they have left work, they could be held liable if the worker is at risk because of alcohol consumed in the workplace, for example at after-work drinks, or at a client function.
Where the responsibility falls will depend on all the circumstances such as closeness of the connection to work, the steps taken by the host and individual responsibility, regardless, I would always recommend putting steps in place to protect both the organisation and its employees.
Rather than focusing on whether the precise wording of the HSWA applies and when, it is more useful to focus on the steps businesses should take when providing alcohol.