The nature of water itself makes some aspects of testing water guns a bit difficult, but I feel good about the process overall.
To start, we need to know how much water these things will hold. I do this by weight. Since 1 milliliter of water weighs 1 gram, it’s easy to measure capacity with a scale. After subtracting the empty blaster weights, you can see in the table below exactly how the capacities shake out. The Nerf Super Soaker Hydra has the overall largest capacity followed by its Super Soaker sibling. The least capacity was definitely the Temi blaster since it only stores the water for a single burst at a time.
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Once the capacities are locked down, I then go through the process of shooting each gun as quickly as possible to find the shortest amount of time possible to empty that capacity. I have help from someone with a timer and sometimes have to do multiple runs. Sitting around and shooting water guns for a couple of hours nonstop is way more of a workout than I expected.
You can see here that typically if it takes a long time (over 30 seconds) to empty a water gun, its overall soak factor (capacity divided by empty time) is pretty low. Although the quickest dump time doesn’t always mean the highest soak factor, that is exactly how it works out with the Temi. With a moderate one-shot capacity at just over 500mL, the 1.8 seconds it takes to empty gives it a massive soak factor of almost 300.
The Super Soaker siblings come in second and third with similar empty times, but the Hydra’s larger capacity gives it a better soak factor. The old-school Nerf XP50-AP and Team Magnus guns have median capacities and low soak factors, but keep you in the fight for much longer than their counterparts.
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The only other measured test we run is for distance. This one is fairly simple in design, but has a touch of abstractness to it.
Holding the blaster at the same starting point, height and angle, I let out several blasts, usually five, until I am sure that I can’t get the water any farther on an outdoor concrete surface, which discolors well with water. I then measure from the starting point to the furthest edge of the water markings — discounting any stray single drops.