Under the Workplace (Health, Safety and Welfare) Regulations 1992 all employers must supply their workers with adequate supplies of clean fresh drinking water.
The drinking water must be supplied by the employer and the drinking water must be readily available at suitable and clearly marked places.
If your employer is not providing you with drinking water you should contact the health department about it and see what they can do.
I've always been supplied with adequate drinking water from all jobs I've worked at and sometimes I've still even brought something else to drink with me.
However your employer must provide you with water at all times.