You might want to use liners. That way, your planting area is always wet. Or use a large container

I recently built a small pond (140 gallons) and added plants and fish. In my filterfalls (waterfall/filter, I placed some small baskets and added water cress. I got the watercress at the supermarket.
In short order, they were growing, and growing. They are think and healthy.
Not only is the watercress helping to keep my pond water filtered but providing veggies for my salads and soups.
If you only want to grow watercress, this would be an expensive way to go but for me it was a side benefit because I wanted the pond and was looking for plants.

Whatever you do, just be careful.

Watercress obviously absorbs the water it's in, & it's a well-known warning when harvesting it in the wild to be extremely sure of the quality of the water it's growing in, as you are eating whatever pollutants might be in that water.

you could just grow it in a bucket with no soil (maybe a small amount at the bottom). I have some growing in my still-water pond, i just bought a packet of organic stuff from the super market and threw it in. It rooted in days and it now completely covers my pond. I'll probably have to throw a lot away because it's so invasive.

Here are some links, one is a commercial operation up in Wichita falls:
http://www.hydroponics.com.au/back_issues/issue50.html

Thinking about this, it looks like cool water and shade might be limitations for you down there, especially in summer. I'm thinking that you could buy several lengths of vinyl roof gutter, partially filled with gravel, arrange them side by side, sloping, but each at a lower level than the last, and connect them together so that the water flows from one to the next, and back and forth. A small pool pump and a reservoir, perhaps a buried tank to cool the water naturally. as the artcle states above, watercress is an "understory" plant that likes some shade. You might have to shut down during the heat of summer. Good luck.
Jay

Here is a link that might be useful: Hydroponic watercress

What is watercress ? is that what they call Kangkong?

You can go to the dollar store or a thrift store & find a porous container that will hold in the watercress. The container should fit in a bucket. Add water to the bucket, put in the container holding the watercress, add an air pump, & it will start the rooting. Clean off any lower leaves, of course, before you put the watercress in. You will eventually need to add hydroponic nutrient, or as Hen11 suggested, devise a system with some soil in it. It should cost you about $2.00 for both containers & $6.00 for a cheap aquarium air pump.
I bought some clearance watercress from the grocery store, cleaned it up, & placed it in my unit. I have it in full sun as it is coming back best that way. As long as it tolerates the sun I will keep it there  if it starts to look bad I will move it to the shade. If the water gets too hot, you will need to cool it, however.

If you put fish in a pond which have earlier shared water with tropical fish, it could be possible to get shigella from eating contaminated watercress in the same pond. My cousin got shigella from tropical fish in a home aquarium, not washing his hands thoroughly after touching the fish. In the wild, if there have been sheep in the area, I have heard that you can get liver flukes from eating watercress. A little caution in setting up growing conditions is in order.

Where at the store would I find water cress? In a bag like lettuce? HELP please

eva65,
>What is watercress ? is that what they call Kangkong?
Rarely... Kang Kong's most common name is Chinese Spinach or Ong Choy.

Tnflower_lover,
It depends on the store. Just as with regular lettuce, it can be sold in bunches, in bags, as separate leaves, as a plant with roots, etc. Just look at pictures so you know what it looks like before you buy...

Here is a link that might be useful: watercress pics

last year at the end of the summer I removed the tomato plants from one of my Garners Supply self watering tomato planters (like earthboxes), and replanted with Watercress seeds. the watercress was fascinated with this pot (which always has water beneath) and grew great until it froze in December. will try again this spring with some window boxes placed in a big plastic container that I will keep filled with water. I love watercress in the salad bowl.

Michael Hewitt
Hampstead, NC

Would kang kong be good for salad bowls, or is it like sweet potato leaves that should be sauteed?