Do all restroom trailers need a fresh water hookup to operate?

No, a restroom trailer does not need a continuous water hookup. The ones we rent carry an onboard fresh water tank that feeds the flush and the sinks, and plenty of park events run on the tank alone. The catch is that the fresh side runs down and the holding tank fills up based on use, not on the calendar.

Here is how I size it for a two day event. Ask the rental office for three things on that exact trailer: fresh tank capacity, holding tank capacity, and roughly how many uses they expect per fill. Those come off the unit's spec sheet, so don't guess. Then hold that up against your crowd. Food and beer push restroom traffic up, and most of it lands in the late afternoon and evening.

For our weekend fests in parks with no spigot, we book a service visit overnight between day one and day two. The truck pumps the waste side and tops off fresh water in the same stop. That one visit has saved us every time. Since a truck can pull right up to your spot, it is an easy add.

Also ask whether the trailer needs power for the pump and lights. Water and power are separate questions, and people usually only ask about one.