Tank type water heaters are very unsafe. Full of germs and other nasty tidbits.
Since you mentioned something related to the cost of "proper" maintenance of tankless water heaters, here is a discussion about the "proper" maintenance of a tank type water heater.
http://www.nashville.gov/water/splash/h2o_heater.htm
Water heater maintenance
Water heaters, whether gas or electric, have become more complex and expensive. They also do not seem to last as long as they once did. This is one modern appliance that we couldn't live without, but is "out of sight, out of mind" until we have problems with it.
Hot water heater flushing
Maintenance books recommend that the hot water heater be drained (flushed) every six months, but few homeowners bother to do this. Often, it is put in an area that is not as accessible as other appliances. It may or may not be easy to drain, even though all heaters have a hose connection and faucet control at the bottom. This task is not only inconvenient, but often the washer and/or washer seat on the faucet must be replaced after draining. Sometimes the entire faucet assembly will have to be replaced. If this is not done correctly, the unit may leak at the faucet. Furthermore, the unit can be damaged while drained. Unless the customer is fully familiar with servicing these units, one should consult their service representatives at the gas or electric utility before undertaking these tasks.
Odors
A heater which is recycled off/on or left off for a period of non-heating may develop offensive odors from sulfur bacteria. The odor is hydrogen sulfide -- "rotten egg odor." This odorous water may be drawn back through cold water faucets as well as the hot water faucet.
Temperature settings
The heater thermostat should be set at a reasonable temperature. Scalding of infants and the elderly can be a real hazard, even when the temperature setting is within proper limits. Again, the user should consult with their energy supplier to have the unit set at a safe temperature.
DO NOT USE HOT WATER FROM THE TAP FOR DRINKING OR COOKING!
Because warm/hot water is much more corrosive of metals than cold water, one should not use the hot water tap as a source for drinking, cooking or dilution of infant formula. It can be high in metals such as aluminum, iron, lead, copper and zinc.
The heater tank also tends to concentrate these metals and precipitate them in layers inside the heater tank.
Many tanks have a metal "sacrificial anode." This is designed to wear down and can be an additional source of metals. While it may be a convenient shortcut, water from the heater is not an approved source of drinking water.
White plastic particles
It is not unusual for the white plastic (PVC) filler tube inside the heater to disintegrate and discharge small white particles to the faucet aerator screens. These particles can come through not only the hot water lines but the cold water lines as well. These particles may appear to be soft and crumbly, but a good test is to heat this material with a match. PVC will melt; minerals, such as calcium, will not.