I love ensata Variegata. They are so vigorous, yet the flower is dainty looking. The leaves retain their variegation all season here.

I would not suggest you plant them in water in your area. I would plant them in soil, and as you said, lots of water. Full sun to very light shade.

I would amend the soil with well composted cow manure and lots of peat moss, no matter what soil type you have. Japanese Iris like acid soil about 5.5-6.5 ph.

Soak the rhizomes in water overnight before planting, and never let them dry out. Water daily for the first week, every other day for the next month or so, and then be sure they get at least an inch of rain or water per week. I keep them pretty moist the first year, especially in the hot summer months.

Plant about 2 feet apart, and leave a 3-4 inch well, or depression all the way around each plant. (To hold water, and since new roots grow ABOVE the old ones, this will help retain the plants vigor for a longer period of time). Mulch really well, at least 2-3 inches. Pine straw is great for mulching if you can get it.

Once the plants start showing new growth you can use a liquid fertilizer, Miracid is good. Once every three weeks or so. Don't otherwise fertilize the new plants the first year. Don't use lime or bone meal.

Next year fertilize early spring, and about a month before bloom, using a 10-5-5 fertilizer or thereabouts.

Divide every 3-4 years, and transplant the divisions to where Japanese Iris have never grown before, with newly amended soil.

Having said all that, they are very easy to grow, and I know you will love them!