NIM02101 - Class 1 NICs: Earnings of employees and office holders: Council Tax, water or sewerage charges: Employer pays all or part of an employee's Council Tax, water or sewerage charges
If an employer pays all or part of an employee’s Council Tax and/or water or sewerage charges, the payment is earnings and NICs are due. The employer is simply meeting the employee’s debt.
See NIM02010 for the meaning of “earnings”.