That's not quite true, water charges are part of your council tax. You get a discount if you have a septic tank because then dealing with the waste water is your responsibility.
But you pay a flat rate based on your property's estimated value in 1991.
And also remember to look up the list of accepted photo ids and get yourself set up with at least one that you can take with you to the polling station. https://www.gov.uk/how-to-vote/photo-id-youll-need