A water garden can add a sense or serenity to any garden, especially if it contains a small waterfall or fountain. Your water garden need not take up much space, in fact a stable water garden (one which won't become overgrown with algae) can be grown in a container as small as 18 inches across. To make your water garden you'll need a few items, most or all which can be found at your local nursery or hardware store.

CONTAINER CHOICES
First, you'll need a container that will hold water. Choose one at least 18 inches in diameter and 10 inches deep. Some excellent choices are:
Glazed ceramic plant container without a drain hole (or plug the drain hole by gluing a piece of metal or ceramic over the hole with water-proof glue)
Fiberglass plant container without a drain hole
Large galvanized tub, lined with plastic or painted inside with rubberized paint
A half wine or whiskey barrel, clean and water-proof or with a plastic liner
Any decorative container, lined with plastic or made otherwise water-proof
Useful cast-offs, like an old sugar kettle or cement barrel

Note that some plants, such as water lilies, will need a container at least 18 inches deep. Research the plants you wish to grow in your water garden and choose a container accordingly.

WATER PLANTS
There are many plants that love a boggy environment or having their roots fully submerged in water. Some, like watercress or water hyacinth, are not planted and simply float on the top of the water.
Here are some excellent choices for your garden:

Floating Plants
Watercress or Water lettuce
Water Hyacinth
Shellflower

Bog Plants
Dwarf Cattail
Japanese Iris
Water Canna Lily
Cardinal Flower
Parrot's Feather
Rushes and other water-loving grasses

Deep Water Plants
Miniature Water Lilies
Water Hawthorn

WATER PLANT CONTAINERS and SOIL
Water plants need to be planted in containers which will allow water and nutrients to the plant roots, but not allow soil out to contaminate the water.
Baskets are often recommended for planting your water garden, be these are best only for large ponds. They can be used for your small garden, however, if lined with a fabric which will not break down and which has a fine enough weave to hold in the soil.
Other choices for your water plants are terra cotta pots or plastic pots which will be submerged just under the water line. Cover the drainage holes with fine mesh screen or fabric to prevent the soil for leaking out.

Plant your water plants in a heavy clay soil topped with sand, or, if available, a specially formulated soil mix for aquatic plants. Plant in the pot as you would any other container plant, then top off with an inch of small rocks or pebbles to keep the soil from floating away. Rinse and soak the soil well before submerging in your water garden.

PUMP or FOUNTAIN
Small fountain pumps can be found at most hardware stores and garden centers, and are widely available over the Internet You won't need much flow or pressure – a 1 to 2 foot head and 50 gallons per hour (GPH) will be plenty for a small water garden. You can go larger if you plant your garden in a barrel or other large container.
The simplest pump is a submersible with a filtered inlet and an outlet for tube attachment. You can leave this pump as is to cause rippling water in your garden, or attach a tube to the outlet and run the tube to just above water level for the gentle sound of gurgling water. You can find these simple pumps on the Internet for as little as $10 each.
Other pumps are available with special fountain attachments, or with small integrated waterfalls. Choose a pump which works with your overall design and that is not too large for your container.
To reduce the amount of cleaning needed for your pump's inlet filter, place your pump in a jar, large enough to allow free water flow but short enough to submerge in your container. This will keep any bottom sludge from clogging the filter intake.
Note: Your pump will need to be cleaned periodically. Whenever you notice the water flow is reduced, unplug the pump and remove it from the container. Follow the manufacturer's instructions for cleaning, then replace in your water garden.

DESIGN IDEAS
Position your water garden container where you want it to remain on your table, deck, or patio. Install your pump or fountain, if desired, and run the power cord out the back of the container.
Add your deep water plants (planted in their containers) to the bottom, or raised on bricks or rocks if you have a deep container. (Position plants at the depths recommended with their planting instructions).
Next, position your bog plants, raised up on bricks or rocks so the tops of their containers are at or just below the water surface. (Refer to the planting instructions with the plants you have chosen). Position tall plants towards the back, medium plants along the sides, and short or overhanging plants towards the front.
After all your deep water and bog plants are positioned, add some rocks and river pebbles to the container for decoration, then float your surface plants in the remaining open space.

Remember to not completely fill your water garden with plants from the start – your plants will grow and fill in throughout the season.

If you have chosen a large container, consider adding a few goldfish or small koi to your water garden.

At first, your garden may develop an overabundance of green algae. Don't be alarmed, the water will soon clear.

Note: if you live in an area with freezing winters, move your water garden to a warm area before first frost, or drain and store for next season.

Gardener's Supply has a wide range of containers, potting soils, and other supplies for your gardening success: