there are filters that you can use to deionise the water... do you have a ppm meter?
well actually the resistance of the water should not change things much because as per stan words if you restrict the amps and use the voltage potential to do the work the water will get charged !
May i ask you a question? If you get a charged conducting sphere that you connected to a source of 1kv positive relative to ground, what is the electric field right next to the sphere? what is the electric field 1m away? what if the dielectric was water?
Now imagine its a hollow sphere, what is the electric field inside?