Most of the self watering pots available in the market, are using the capillary action of water. They are fairly expensive and cannot be easily made at home.
There is a lower compartment in each pot for storing the water and a tube for connecting the lower water filled compartment to the upper compartment of the pot which contains soil, mulch and a plant
The empty plastic bottle method is fairly cost effective as the waste bottles are recycled. However this method is mainly suitable for large size pots and time is required to experiment, so that water is released slowly