The incident occurred early this morning on the R680 Cork Road at around 1:20am.
The 15 year-old-boy was pronounced dead at the scene. A second teenager, also on an e-scooter, has been taken to Waterford University Hospital with serious injuries.
There were no passengers on the bus at the time of the collision and the bus driver was uninjured.
The teenager's death is the most recent of 91 deaths on Irish roads this year so far.
The Cork Road is currently closed from the South East Technological University to the Ring Road for a technical examination of the scene. Local diversions are in place.
The news comes following the ban of the use e-scooters for under-16s earlier in May.
Adults are permitted to use e-scooters on roads as long as they comply with regulations. E-scooters cannot exceed a speed of 20km/h and are not permitted to be used to carry goods or any additional passengers.
In 2023, the Gardaí recorded over 220 e-scooter related crashes and collisions, with 54 resulting in serious or fatal injuries.
Furthermore, according to Garda figures, there were an average of 14 e-scooter crashes or collisions every week .
The RSA started a campaign in may to educate young people on how to safely use e-scooters. It included information on age restrictions, speed limits and vehicle specifications.
Gardaí are appealing for any witnesses of the collision in Waterford, particularly any road users who may have camera footage (including dash-cam) and were travelling on the Cork Road in Waterford city between 12.45am and 1.15am, to contact Waterford Garda Station on 051 305300, the Garda Confidential Line on 1800 666 111 or any garda station.
