Hi Annapet
The BWB's(bottom watering buckets) are quite easy to make...and cheap.
Basically its two 5g buckets...one sitting inside the other. Naturally there is about a 3" or 4" gap between the bottom of the top bucket and bottom of the lower bucket. That space becomes the "water reservoir" The top bucket holds all the potting mix and has a "whicking basket" that extends down into the "water reservoir" and whickes up moisture to the potting mix.
Here is a copy/paste from a thread I posted in at Garden Web
I used the two bucket method. Simple, and at $2.50 a bucket....what the he!!
Using the two bucket method you get the advantage of the full 5 gallons for the potting mix. I used the lid with a small cutout to act as the mulch cover.
Drill a bunch of holes in the bottom of one of the buckets except for in the center where you will make a cutout to fit your whicking basket.
You can use many things for the whicking basket, I used a small 10oz plastic cup that I used for my seedlings. Or you could use some PVC pipe like imstillatwork says.
I used a heated nail and poked about a million holes(ok. not a million
in the cup to turn it into a whicking basket.
Your whicking basket should be the same heighth as the gap between the two buckets so that it sits on the bottom of the lower bucket when inserted through the hole in the top bucket and sits flush(or close to flush) with the bottom of the top bucket.
Drill the applicable size hole in the bottom of the lower bucket on the far edge to insert your fill tube. I used a piece of 1/2 sch40 PVC, so a 3/4" hole was right for me.
Drill a drain hole in the lower bucket about 1/2" below the bottom of the upper bucket so there is airspace between the soil and water resivore.
To fill
First fill the wicking basket with wet wet wet potting mix, again, wet wet wet and pack it in there really tight. You want that initial mix in the whicking basket to be super saturated and packed reaaly tight in there.
Then fill the bottom water resivore(you want to start the whicking action.
I then put a layer of mix about 1/2" deep in the bottom of the bucket and wet it dowm. I them cut out a circle of landscape fabric to install before I finished filling as I want to try and keep the roots from penetrating down into the water resivour. This is a purley optional step.
I continued to fill the bucket with mix about 2" at a time and wet it and lightly packed it as I went.
When the bucket is about 2/3rds full, add 1 cup of Dolommite Lime and mix throughout the soil.
Once the bucket is full, I made a small indentation around the perimiter of the soil to add my cup of fertilizer. You dont mix it in, just put it on top.
Plant your plant. I used the lid as my mulch cover. I just cut a hole in the center of the lid and carefully slipped the plant through the hole