I have a non separated water meter - Can I pass on this cost to the tenant?

Technically speaking you cannot because you don't know the exact amount of water your tenant is using.

However the best way is to include water usage as part of the rent. So when you advertise your property include in your description “Water usage is included in the rental price”. You might put on an extra $5 per week for water usage depending on the average cost of water usage in your your property (check a recent bill to find out).

In Queensland you can nominate a specific amount of water that will be charged to the tenant on an regular basis.