The least expensive normal gas water heater I see on Home Depot's web site is $430 or so, and is a tiny 29 gallon unit.    

I would say 15 gallon landscaping and find out what us most popular look for your area. 

Built/welded all the large multi million gallon water tanks on the base that supply the base with water.

I have seen water companies raise per gallon water and sewer rates now that economy is recovering.

I did a cat pee house flip and it was horrendous. the cement was so bad in the garage where she kenneled cats .. we used peroxide from a beauty shop by the gallon, pored it on the concrete to lift the odor out up from the concrete and did several applications,, rinsed with water,, and then used odor medic, expensive, and then ozone machine, and then painted the floor. took like 4 weeks to get to the point where we could tolerate the garage to be able to smell a difference.. we honestly thought about tearing up the cement floor in the garage it was so bad. 

All while working as humble teachers in a city where a gallon of milk can cost $8!

Home Depot is amazing for a flipper because with the gas rewards you can get gas for 1 cent a gallon!

I'm not sure how many gallons it uses per cycle, but I can do some googling to find out.

You can get a sprayer from harbor freight for < $200 and might be able to squeeze out just one gallon with a 211 tip (the sprayer comes with a 517 (exterior)).  

Pipes are generally galvanized in material.Water Heater = There is only one 40 gallon tank in basement for the whole house.Questions: I don't have money for too large of a rehab project.