Water barrels, pots, urns, tubs, baths, vases, and so on, whether self-contained units or linked to a larger pond, really add a different dimension to the garden.
Any container that can hold water is a potential above-ground pond but it should, of course, be ornamental and decorative.
These containers can be placed almost anywhere in the garden but, because they are small in comparison with a whole pond, it makes sense to site them near a sitting area, or where people will spend an amount of time: on a patio, path, or close to house windows would be suitable sites.
Placed to brighten up a dull corner, they can make perfect alternatives to pots of annuals and conifers.
The most important factor is that of light, particularly if you're anticipating growing flowering water plants such as waterlilies.
Do not site the container in a dark corner, but nor should it be in full sun for the hottest part of the year, otherwise evaporation will become a problem.
Another factor is that of running power out to the container, for you will almost certainly need a pump to move the water.
Many of the metal, plastic or ceramic containers in the above-mentioned styles will be watertight, but water barrels - or more correctly half-barrels - could well be authentic old-style barrels made by coopers, where open air exists between the wood slats.
In this case, we need to make judicious use of the familiar PVC liner.
For relatively little outlay, a container water feature can become an attraction, a talking point and, almost, part of the family.