Select a location for your water garden that receives full sun six hours or more per day. Place the water garden container in the desired location--it will be quite heavy and difficult to move after it is filled with water. The container should be 12-to-24 inches wide and 12-to-26 inches deep.
Fill the container with rain water or tap water, and let the water sit for 48 hours to warm up and allow any chlorine in tap water to dissipate.
Fill a 6-inch plastic pot half way with clay soil or commercial aquatic potting medium. Insert the roots of an upright bog plant such as arrowhead, blue flag iris or dwarf papyrus into the pot. Holding the plant upright, fill the pot to 1 inch from the top rim with additional soil or potting medium.
Fill a second, 6-inch plastic pot with clay soil or commercial aquatic potting medium to 1 inch from the top rim. Insert an aquatic plant rhizome (lotus or water lily) at a 45-degree angle near one edge of the pot, with the growing tip angled upwards.
Poke two aquatic fertilizer tablets into each pot. Place 1-inch pebbles on the surface of the soil or medium.
Place bricks on the bottom of the water garden container to a height that allows the two pots to sit with their rims about 6 inches below the surface of the water, if your container is deep enough to require it. Set the planted pots in the pond.
Release the snails into the pond. Place a floating aquatic plant such as water lettuce, water hyacinth or giant velvet leaf in the water.
Wait three or four weeks for the pond water to cloud with an algal bloom, then one additional week for it to clear. Insert a low-flow water pump into the pond and arrange tubing to bubble water out at the surface of the pond using a binder clip or baling wire to hold it in place; a pump is not necessary unless you are going to plant additional plants or insert substantial numbers of fish.
Add fish, if desired, after the water has cleared from its initial algal bloom. Consult your fish supplier for appropriate numbers of the variety of fish you are using. Feed fish a small amount of fish food daily.
Add rainwater to the pond weekly or more often, as necessary, to make up for water that evaporates.
Move the water garden indoors when temperatures fall to 40 degrees F. Prepare a tub of rainwater or tap water indoors as you did to start water garden. Lower the water level to the minimum amount to hold fish; if you do not have fish, empty the water completely, then carry the tub to its indoor location. Refill with prepared water.
Alternatively, move any fish to an indoor aquarium. Drain the pond. Discard or compost the floating aquatic plant (or place in an aquarium with fish), and place potted plants in a basement or garage where they will not freeze, but remain dormant over the winter. Re-assemble the water garden and replace the plants after temperatures rise again into the 40s.