Natural swimming pools

Here's something that has really inspired me!

We all know that chlorine is highly toxic to life, it is used to stop bacteria and algae from growing in swimming pools.
Managed properly, natural swimming pools have crystal clear water and require no chemicals to maintain, as they are self-cleaning mini-ecosystems.
The use of aquatic plants to absorb the nitrates in the water keep it from stagnating!
 more info here
Daniel Tohill at www.sustainablehabitats.co.nz has built a couple around New Zealand.

Asteraceae

The Asteraceae or Compositae, ("aster" means "star") also referred to as the aster, daisy, or sunflower family, is the largest family of  vascular plants.  Vascular plants are those containing lignin in their stems. Lignin is one of the most slowly decomposing components of dead vegetation, contributing a major fraction of the material that becomes humus as it decomposes. This obviously makes these plants excellent for mulch.
This family includes medicinal plants such as arnica, burdock, boneset, calendula, chamomile, chicory, mug/cronewort, coltsfoot, dandelion, echinacea, elecampane, feverfew, goldenrod, gravel root, grindelia, liferoot, milk thistle, tansy, yarrow, valerian, wormwood, and wild lettuce.
It offers us delicious foods: sunflower seeds, lettuces, true artichokes, sun chokes (also known as jerusalem artichokes), escarole, and endive. And, it is one of the landscaper's favorite families, for many Asteraceae--such as chrysanthemums, dahlias, bachelor's buttons, daisies, cosmos, coneflowers, goldenrods, sunflowers, zinnias, and, of course, asters--bloom for months with colorful hardy flowers, and many are perennial, too.
The older name for this family tells the tale more clearly: Compositae. Each bloom is composed of hundreds of tiny flowers. With a hand lens, you can look closely at an Asteraceae blossom and see the many tiny flowers crowded together that make up the larger "flower."

  

Apiaceae (or Umbelliferae)

The Apiaceae or Umbelliferae is a family of usually aromatic plants with hollow stems, commonly known as umbellifers. It includes cumin, parsley, anise, carrot, coriander, dill, caraway, fennel, parsnip, celery, Queen Anne's lace and other relatives. It is a large family with about 300 genera and more than 3,000 species.
The cultivated plants in this category are almost all considered good companion plants, as the umbrella of tiny flowers attracts omnivorous beneficial insects, especially ladybugs, parasitic wasps and predatory flies, which then will hunt insect pests on nearby crops.

The root of these plants is a tap root so it will generally be non-competitive in the garden.
Here's an excellent selection of plants with many uses. The sky is the limit!