Flammable meaning it is able to become a flame, would be no, but let’s try to find a way, and a reasoning.
A flame is plasma of elements and molecules when so hot they are beyond a gas state, usually from an oxidation reaction. Burning, is when something is hot (jiggling and flying fast) enough the forces binding the atoms are overcome and they separate, making opportunity to re-combine with oxygen to form a lower energy molecule, releasing the old bond as radiation and kinetic energy. This can become “runaway” oxidation (a fire) until no more fuel and-or heat can sustain it. Other words: stuff moves so fast it falls apart and oxygen swoops in and makes new things that speed up more things.
Burning can turn to fire/flame when the energy released from oxidation and the decomposed particles are so hot they go beyond gaseous to plasma state and the radiating light is what we perceive as flames.
Water proper can’t really burn as burn entails oxidation and decomposition of the molecule. Water as the bonded H2O won’t break down if oxidized as we would expect for burning, it would be hydrogen peroxide and really just oxygenated water. With that, water is oxygenated hydrogen and so an oxidation product already, making water like the ash of a hydrogen fire. And electrolysis of water to H and O, is like turning ash to fuel.
For water to be flammable, i.e. become a flame, we would need plasmatic ions of H and O directly from H2O. I believe if you energized water thermally/kinetically you would never be able to do this, if you used electrolysis you wouldn’t be making water flammable but decomposing it into flammable constituents that. I think the best hope is to have a special container that can heat the water to plasma, but this is likely a manipulation of definitions more than a flame of water.
From all this I can’t justify saying water is flammable. There is no practical ignition temperature or flame state. Water can be processed into flammable things but is not directly flammable.