You need to know the rateable value of the property.
https://www.nwl.co.uk/myaccount/your-bi ... explained/Have a look a the charges guide pdf on that page.
For example my bill from that water company is as follows:
Water
Fixed charge 365 days at £146.44 per year
Rateable value £338, at £0.8513 in the £1 = £287.74
Sewerage
Fixed charge 365 days at £179.20 per year
Rateable value £338, at £1.0322 in the £ = £348.88
Just over £96 per month for 10 months.
If you know your rateable values of your own property, they should be on your current bill, then apply the rate in the £1 to the water and sewerage parts, add in the standing charge and you will have what it will cost for Northumbrian Water.
This is for a large 4 bedroomed house, double garage etc.
Hope this helps?