Choosing between a tank and tankless water heater in the Phoenix area involves more than brand preference. Arizona’s warm groundwater temperatures, hard water conditions, and high summer energy costs change the math compared to cold-climate states. Gas tankless units offer 24-34% efficiency gains and 15-20 year lifespans but cost more upfront and need annual descaling. High-efficiency tank and hybrid heat pump units often make more sense for larger households with simultaneous demand. Federal tax credits up to $600 apply to qualifying units in 2025, and utility rebates from APS and SRP can offset additional costs. Permits are required for most replacements in Scottsdale. Matching the right system to actual household usage – not just following general advice – is what drives long-term savings in an Arizona home.