It's fine! But yes — in its full-power form, pulsefire is nigh impossible to put out when it hits a living being. However, as Newt makes it less effective, it will be able to be put out, but that still needs more effort than putting out a regular fire — so think ice instead of water, or cutting off its "oxygen" aka its connection to the effect of the suns/moons, which can be achieved with a strong physical barrier or something else that removes any kind of light.