Hi @Ben Durwood,
I agree with @Tim VandenToorn that there are a lot of factors to be considered in determining whether some of these costs can or should be passed on to your tenants. Also, I think you are smart to challenge your property management company on this.
I have a duplex in town and for that property, the water isn't separately metered and additionally, I also cover the cost of snow removal and for mowing the lawn, because there really isn't a good way to split those amounts.
However, I also have a single family home in which it's built into the leasing agreement that the tenant is to cover the cost of water. The PM company that I use pays for the water to make sure it's covered, then I see a credit come through after the tenant reimburses me for the cost of the water. The fact that the tenant is covering the cost of water didn't seem to have an impact on the rent that I was able to get either as my rent for this property is solidly toward the top of the market.
It's definitely a smart move that you are scrutinizing and challenging your operating expenses. Also, if your management company isn't willing to think outside of the box a bit with you on this one, it might be a red flag.