If you do the work yourself you will still need certification that everything is correct. Usually a plumber. It is a one-off cost.
Saving packaging is fine, but there is no proof that those devices were actually fitted to the property leased.
Marg
To charge water consumption in Qld you must have the property certified water wise and it MUST be mentioned as a condition in the lease.
So no, you cannot claim for water usage from this tenant.
Marg