The strata Act is quite clear on this – levies and special levies are to be paid based on unit entitlements, unless you get an order from NCAT to the contrary.
If there is a majority feeling that the single tenant landlord has been seriously disadvantaged, there is nothing I can think of to stop the owners corp making a one-off pro-rata payment by way of restitution.
Between that and the reduced bills in the future, the landlord should be happy to pay the legislated share of the levies to have the water meters installed.