water is one the the most important resouces that we have on this planet. making a correct use of it is fundamental to mantaning this planet as a living planet that can hold the richeness that this one has.
on a urban farm context, is dificult to maintain the water balance on your plants. it's important to understand that if you lose water on the drainage system your farm is also losing nutients. avoid big rain falls and execive watering. the level of moister on the soil it's influenced by your climate profile, size of your container, type of soil, type of vegetables, plan life cicle, etc.
here you can find passive watering systems, systems that don't use energy to work. if you need a more precise control and sensors data check the nano and mini vacations electronic boards. they were designed with this monitoring systems in mind.
here are diagrams on how to setup the diferent parts of a watering system with diferent configurations and materials.
1 water pump; water under the soil; 2 holes on the bottle
1 water pump; 1 tennis ball; water under the soil; 1 hole on the bottle
1 water pump; water under the soil; multiple bottles
1 water valve; 1 tennis ball; 1 hole in the bottle; water above the soil