The water's electrification wasn't the only problem.
But the electrolysis.
The hydra had subjected the water to an electric current with enough power to separate the hydrogen from the oxygen in the water, thus creating a deadly combination of gases.
Gerald got distracted checking that the water in contact with his feet hadn't been electrified, which wasn't the case thanks to the magical barrier.
However, the danger was outside, where the water had transformed into a deadly cocktail of flammable gases ready to explode.
The hydra didn't hesitate a second and spat a great burst of fire from its mouth which upon coming into contact with the oxygen and hydrogen exploded.
An immense explosion was released. Though the resulting energy from the reaction was mostly transferred in the form of light and heat, the shockwave was strong enough to destroy the magical barrier and send Gerald flying far away.
