The first step is to call and book an assessment. If you have extended health, then you may want to check to see if a referral is required by your insurance company to have your receipts reimbursed. As physiotherapists are considered primary health care providers, you are not required to have a referral in order to attend.
After your assessment, your physiotherapist may recommend that you get some treatments to address any muscle imbalances or specific weaknesses before you begin hydrotherapy. Make sure to mention that attending hydrotherapy is one of your fitness goals when you discuss your concerns with your physiotherapist.