Chicken and egg situation re rent increase or change contract.

Tenancy Deposits

I've inherited a tenant who has been in property for 8 years paying the same rent throughout. Her contract states that the landlord pays the water rates. The tenant pays all other utilities and council tax. I want to increase the rent and offer a new fixed term contract.

Can I get her to sign a new 6 month contract that now makes her liable for the water rates? Is this change something which I should point out to her? Would I then give her 6 months notice at this time of a rent increase?

Or would I give 1 months notice of a rent increase as per periodic agreement and then sign a new contract re; water rates after this?

The rent increase is priority but I want to do whichever is proper.

Thanks in advance for any help.

Fiona