Due to the construction and placement of the battery pack, it is difficult to reach the the fire in many types of EVs/
ctif.org
A ladder or quint company may have a tank as small as 250 gallons, while a tanker may carry up to 3,000 gallons or more. The tanks have baffles inside to prevent the water from sloshing around too much while the truck is moving.
A typical internal-combustion engine, if ablaze, takes about 500 to 1,000 gallons of water to fully extinguish
An interesting fold to this issue is that as a whole, EV's are significantly less likely to catch on fire compared to an ICE vehicle. So while they take significantly more time and water to put out, they are still much safer(with regards to catching on fire) than ICE vehicles that catch on fire all the time, comparatively. For every EV fire on youtube, theres about 10,000 gasoline fires you dont hear about.