Here's where things get fun. Just like the number of reps, 3-6 sets is the best range of volume for this training method. If you like your workouts paced like clockwork, take 30-60 seconds rest between each exercise.
The natural attraction between positive and negative keeps the ions surrounded by water molecules and therefore dissolved in solution. Many biochemicals are either polar molecules or charged ions (or both) so water makes an excellent solvent for them.
Pure water is an insulator, since it doesn't contain any charged particles to act as conductors. However, water is an excellent solvent for charged particles like salts, so it's unheard of to find pure water in nature.