(hot water is a small cost) with large out of pocket expense to purchase & install. you're using hot water all the time at home. the limitations of these are multiple simultaneous hot water sources running at once - some could/will have insufficient hot water (ie. shower and dishwasher on at same time).
gas versions typically need to vent directly outside (might be an issue)
Well, a gas heater/geyser may be relatively cheap, but electric geysers are the story of the month here. The electric utility started 'load shedding' (how's that for trying to make 'blackout' sound planned?) three weeks ago, and then the story came out....
Ten years ago the utility approached the government and told them capacity was shrinking, with a watershed due in 2007. The government told them they could NOT build further plants. The inevitable happened.
Hot water is suddenly a hot topic; the utility is begging people not to use its product (I think their marketing strategy is a bit iffy myself), and energy saving is paramount. Main culprit - you guessed it - geysers. Partial solution - the local authority fits 'ripple units' to every geyser (about 700 000 of them locally) in the system; power usage climbs, a signal is sent down the wiring and they all shut down. Considering the load on the West Coast of the USA, much of Canada (I believe), much of continental Europe and definite burdens almost worldwide, wholesale implementation could save an immense amount of power immediately.
In the meantime, you could - 1. fit a geyser blanket; 2. turn down the maximum temperature, or 3. fit a timer (if it's an electric geyser) - I had the last one in mind anyway, but since it's an electric timer and since we're already experiencing the power cuts, you can probably see why I'm reluctant.
I had relatives in a house that used an in-line water heater and they had their drawbacks. High pressure hot water was out of the question, and at low pressures what came out of the pipes was almost live steam. You had to be very careful and, with children around I thought them pretty dangerous.