How do I build a water drip system for my balcony plants?

Depending on your plants one of the simplest things to use are inverted soda bottles. Fill them up, put the lid back on and put a small hole in the middle of the lid. Sink it into the soil far enough to stay upright and it'll even tell you when each plant needs water

You can buy these systems on ebaay or Amazon or garden sections at large DIY's or Garden Centres or use upturned plastic bottes as drip feeders to each plant.

You probably could. I’d head to the plumbing aisle of your local home improvement store, look for tubing and valves, plus something to use as the water holder.

https://www.youtube.com/watch?v=jeA1W2XR4ss