If you have many plants in your garden that need watering you can of course simply pour water from any container but building a thumb-controlled watering can gives your plants a gentle distributed flow of water, keeps a plastic container of a landfill, and is fun to operate.
Green project weblog Fun in the Making shares how earthenware thumb pots using the same principle were used in 17th and 18th century English gardens. To make a modern equivalent all you need is a plastic liquid container such as a milk jug. Drill small holes (perhaps 1.58mm) all around the base of the container and driller a larger (5.55mm) hole in the cap for your thumb.
All you need to use the watering can is to place the container in a bucket of water, let it fill for a moment, and place your thumb over the hole on the top -- the same principle behind putting your thumb on the top of a drinking straw. Cover the thumb-hole as you lift the container and move your thumb when you want to release water. Photo by The Burlap Bag
Cool Thumb-Controlled Watering Pot Made With Recycled Materials [Fun in the Making via The Burlap Bag]