I'm designing a DIY water farming system. The ideas come from the zengrow.com machines, which have a very simple working principle. It doesn't suit all edible plants as is, but is great for the kinds that you can buy pregrown in little plastic pots.
Btw. I'm in no way affiliated with zengrow.com, they just happen to sell useful stuff ;). Another good source is http://gb.eurohydro.com/waterfarm.html and their distributors.
I've now printed the tube connector. It feels good, we'll see how much it leaks :). A bit of leaking doesn't hurt, as long as most of the water goes where it should be. Another concerns is how noisy it is, since my hacked up system was horrible in that regard. Now I'm printing the plant holder...
It works! See the new pics. I've compactified the plant holder parts, but it's still too big for these containers that I have, and not strictly necessary, as can be seen from the pics. But especially for bigger non round containers, it should be useful for guiding the tube.
I've now got the prototype working, we'll see how the plants like it. The first one is sprouting already.
All the openscad code is in https://github.com/elmom/scad ATM. The files here might not be the latest! The code uses the MCAD lib, which comes with the code if you just do a 'git clone git://github.com/elmom/scad.git'. Of course you can get them separately too: https://github.com/elmom/MCAD
An instructional 3D model is uploaded too. It might not make much sense, please comment :). More photos here: http://picasaweb.google.com/tuorepuristettu/Hydroponics
Info for the plant-holder from the code:
// This is a holder for plants, to be used for indoor gardening.
// Idea is from the zengrow.com systems.
// This should hold the plants in holes made to the lid (or other sheet)
// of a water container. A pump pumps the water through a tube, and the
// other end of the tube is held over the plant. The water then returns
// to the container after passing the plant's roots.
You will need the container (ask for large used food containers from the local bakery etc.): height 15-25cm, the other dimensions at least 25cmx25cm (about 10-30 litres). Then a pump (buy from zengrow.com or find some aquarium pump), some tubing (about 10mm ID) and a water divider (see the printable tube connector). You can then grow stuff from seeds or make your store bought veggies grow some more. A sponge like growing media (as available from zengrow.com) is better than dirt, but some kind of gravel might work too.
For year round farming in most areas a proper lamp is a must. The ones from zengrow.com are good, but anything with similar specs should work.