Typically, tank water heaters are the more popular option among homeowners across the country, but this is largely because tankless water heaters are a fairly new thing. The decision of which type of water heater is right for your property depends on several factors, one of which is the question of how much water you typically need. Tank water heaters typically store between 20 to 80 gallons at a time, but can use more energy due to the fact that they are continually heating a full tank of water for later use. With tankless water heaters, you're only using energy to heat your water as you actually need it, but the system itself is a bit more expensive to install than a traditional tank system.