Although it is not a formal legal requirement like an EICR or Gas Safety Inspection, a Legionella risk assessment is recommended to landlords in the government's How to Let guide.
Landlords do, however, have a general responsibility and duty of care to their tenants that includes making sure there are no health and safety hazards in their rental property.
If ingested, Legionella can cause Legionnaire's disease and make your tenant very ill. A Legionella risk assessment is an ideal way of ensuring your water supply is safe to drink and use.
Learn more about Legionella assessments: A Guide To Landlord Legionella Risk Assessments