No matter what, run all incoming water through a water softener- that sounds NASTY!
If green's your goal (either carbon or cash-savings), in FL between state rebates and federal tax incentives (as well as some local city & utility subsidy) solar hot water with electric-element for backup can often be had for similar money to a whole-house propane tankless install. (It just doesn't take all that much solar collector to work in FL, and it doesn't need to be an overly complex freeze-protected system since freezing weather is typically brief and none-too-deep.)See:
http://www.dsireusa.org/incentives/...FL33F&State=federal¤tpageid=1&ee=1&re=1
If endless hot water is your goal, solar doesn't cut it any more than any other tank though.
But for long showers (and NOT tub-filling) the capacity can be effectively doubled with a shower-drain heat-recovery heat exchanger like a GFX or Power-Pipe (for about $500-700, works with any hot water heater.) see:
http://www.renewability.com/uploads/documents/en/home_retrofit.pdf
http://www.renewability.com/
http://www.gfxtechnology.com/VGFX.html
It may take a decade to pay for itself on utility bills if your rates are cheap, (but it surely will in marital-counseling costs after numerous cold-showers avoided.
) In more expensive water heating situations (like running an electric tank heater @ 20cents/kwh in cold-water MA) the payback is within a very few years.
Since it's a counter-flow heat exchanger the water flow has to happen at the same time as the drain flow to get anything like full benefit, which is why putting it on the drain from the main shower is key. If there isn't enough headroom for a tall one (as is the case in many FL homes), short fat ones can work as well- it's the total surface area that's key to performance. (A 48" 4-incher works about the same as a 60" 3-incher, etc.)
In a few cold-water states they're offering rebates on 'em for the energy savings (WI kicks back $400 on these for electric-tank users!) but energy-savings aside they can be worthwhile in houses where you don't have the space for an 80-100 gallon tank and you have 3-4 people who want to take showers in succession.
In combination with solar it boosts your solar fraction, with gas/electric tanks it doubles the continuous/successive shower time, with a tankless it gives you higher effective-flow (you can run the laundry & dishwasher without freezing the person in the shower, since the shower is using only half as much hot-flow and it's incoming water temp is higher) In warm-water FL it turns a typical 30-35kbtu/h propane or gas tank HW heater into a continuous flow shower heater, pretty much as-good-as a tankless for that purpose. There are plenty of situations where the expense can be rationalized completely independently of energy costs, if showers are a big fraction of the hot water used. (Showers typically account for ~40% of hot water use in 3-4 person households.)
But if you live in a slab on grade with the shower on the first floor retrofitting one might be tough, eh? ;-)