If your herbs are being attached by spider mites (tiny critters that can be seen best with a magnifying glass), you'll see foliage speckling, dying back and eventually showing webbing. It usually takes a lot longer than three days for plants to go from good health to "completely dead", so I wonder if there's something else going on.

If you conclude you have spider mites from looking at pictures in books or on the Internet (try a Google image search), you can use sprays of water to sweep the mites off the foliage (especially undersides of leaves) and use insecticidal soap to kill/discourage them. There are so-called organic miticides, but I haven't found them to work.

Fish tank water can be used to water plants once in a while, but I wouldn't make a weekly habit of it (herbs don't need or want a lot of nitrogenous feeding).

You should be able to get more help on the Herbs forum (Herbalism is set up to discuss medicinal uses of herbs, not plant culture).

Good luck.

eric, that was a very nice and polite response. You should feel very good.

Eric i totally agree that herbalism is for the discussion of the medical use of HERBS. So get a life and talk about the medical use of herbs and quit preaching about the greatness of the Medical American Health Care SYSTEM. I will when you do. It's not what it's cracked up to be.

Use herbs with wisdom. Know what you are taking with prescription drugs as well as with herbs. Google what you take. Know the side affects. What it does. What it interacts with.
The life you save may be your own. Don't trust a doctor to know.

I second the suggestion to ask in the "Herbs" forum. You can also search through the back posts for that forum. Many topics such as mites and over-watering (a common problem with herb plants) have been discussed at quite length.

I suspect the webbing is a red-herring and you have another problem like over-watering or the plants just getting overly baked in the hot sun. The plants you mention love the sun and drier conditions but desert temperatures and sun may be a little too much for them. Look for the plant's heat-zone rating and compare your own. According to the American Horticultural Society, Phoenix is a heat zone 11 and that is beyond what many plants can comfortably tolerate. Check with other gardeners in your area and see what they do to help their plants deal with your growing conditions.

FataMorgana