Write to your water companyNothing is sent. Nothing is stored.
Why complain?
Your water company has 10 working days to respond in a way that actually addresses what you asked11. If they miss or ignore it, you can escalate to the Consumer Council for Water9 and then to the Water Redress Scheme, which can order a refund or compensation10.
It also forces them to check your specific bill. Meter misreads and split-period calculations across the April rate change are exactly the kind of thing that get missed when nobody's looking. You might find an error worth more than the stamp.
In Kent, wastewater is always Southern Water. Water supply can be Southern Water, South East Water, or another provider depending on where you live. If you're not sure, the canonical check is the Water UK postcode finder14.
The letter
Fill in the form. The letter will draft itself as you type.
Sending
Email to customerservices@southernwater.co.uk, or post to Southern Water, Customer Services, PO Box 41, Worthing BN13 3NZ.
Keep a copy. The clock is 10 working days. If there is no reply, or the reply doesn't cover what you asked, escalate to the Consumer Council for Water.