It takes a while for the water to heat going to the tankless water heater and in doing that, a lot of water gets wasted. Is there such a thing as a pre-heat switch that would start the heating process prior to the water flow activating it? Is there anything that would reduce the amount of water being wasted while waiting for it to get hot enough (like for a shower)?
That would be a tanked system with a recirculation loop but what you save on water you waste in power consumption. The best alternitive would to purchase a point of use heater they are smaller and lower flow than the whole house model but other than that not running without flow is how these tankless units save $.