commercial office unit : Got a Water Rates Bill - Haven't got Keys back from Tenant

My Uncle has a commercial office unit that was rented by a local development office that is connected to the County Council. They gave notice of moving out on the 15th of April. They moved their equipment and furniture out but they still haven't returned the keys to my uncle since they still have to refurbish the property as per the lease conditions. My uncle has requested that they do this and has met with them twice to ask them to do this.
My uncle has just received a water rates bill from the council from the 15th of April for 800€. I presume the tenant should be liable for this rather than my uncle. He just wants to be extra sure before he challenges it since the tenant is so closely aligned with the council. Is there any particular legislation that points to this area?

Well, yes that is the usual thing - tenant pays water usage. But was there any written contract/lease agreement which said commercial and water rates were extra ?
It may seem so obvious that landlords may neglect to state this, but if it wasn't stated and the tenant plays dumb ("you never said anything about water being extra")......??

I assume that tenant paid for electricty? If so your uncle has a stronger case.

What's "closely aligned to the council" got to do with anything?

The tennant had been paying water rates throughout their tenancy as per the lease. It's that they have given notice to us and have obviously said to the council that they have moved out but yet they still have the keys and haven't refurbished the property as per the lease. The fact that they are closely aligned with the council could suggest that the council will be biased towards them in any wrangling.