Physical mechanisms for streamer initiation and electrical breakdown in water are discussed. The focus is on various processes that could lead to the inception and propagation of streamers in water. Physical details associated with observed disparities in breakdown at the anode versus the cathode, differences in luminosity, and variations in streamer propagation speeds are discussed. Creation of a localized low-density region near the site of a field enhancement is shown to be essential for streamer initiation. Finally, the use of a trigatron-type electrically triggered switch with a triple-point geometry is shown to be a low-cost, compact alternative to laser (or acoustic) switching. Such controlled breakdown could be used for various applications including water purification and bio-decontamination.