How do I choose a travel water bowl that doesn't spill?

A bowl with a raised inner lip around the rim slows water from sloshing straight over the edge during braking or cornering, working on the same principle as a splash guard, and pairing this with a non-slip rubberized base that grips the car floor or seat reduces sliding, which is often what causes a bowl to tip over in the first place rather than the water itself splashing out. Bowls designed to clip into a fixed holder or strap to a headrest remove the sliding problem entirely, since the bowl cannot move regardless of the vehicle's motion.

For a bag or backpack, a fully sealed, screw-top or zip-lock style bottle-bowl combination prevents any leakage while in transit and simply opens into a small bowl shape when needed, which suits a hike where the water needs to survive being jostled around inside a pack for hours. A simple collapsible fabric or silicone bowl, while not leak-proof when full and left standing, works well for quick offer-and-pack-away use during frequent short stops rather than for carrying pre-filled.

A wide, low, and heavier-based bowl resists tipping far better than a tall, narrow, lightweight one, since a lower center of gravity and a broader footprint both improve stability whether the bowl is sitting on a car floor, a picnic table, or uneven ground. Silicone bowls in particular often combine a wide base with enough flexibility to wedge slightly into an uneven car floor mat, adding a further layer of stability.

A car-focused setup benefits most from a clip-in or weighted bowl kept as a semi-permanent fixture for the trip, while a hiking or walking setup benefits more from a lightweight, packable, leak-proof design that can be stowed dry and filled only when needed, so choosing based on your dominant travel style rather than trying to find one bowl that does everything perfectly tends to work best.