A top load water dispenser is a type of water cooler that uses a gravity-fed system to dispense water. The unit has a large reservoir of water on the top, which is connected to a small, refrigerated compartment on the bottom. When you want to dispense water, you simply open the spigot at the bottom of the unit and gravity does the rest.
Top load water dispensers are typically less expensive than their bottom-loading counterparts and they're also easier to maintain since there's no need to regularly clean and sanitize the inside of the unit. However, one downside is that they can be more difficult to refill since you have to lift up the heavy reservoir of water in order to do so.