You will need a water bottle
And a nail... (I don't know what size this nail is. You can just eyeball whatever nail you use. Just remember the bigger the nail, the quicker the water leaks.)
Take the lid off the water bottle
Place the nail at the center of the lid
Hammer the nail through and then remove the nail
Full with water and replace with the altered cap. Make sure to not fill to the top. Also, once you tip it, be careful of a little stream of water that may come out.
Bury the waterer (top down) into the dirt of the plant. Try to be close to where the roots are.
And there you are! This should last about a day or two depending on the temperature outside. If you need it to last longer, use a 2-liter soda bottle instead. Enjoy!