If your container is 30" above your garden, you will have 1 pound of pressure minus a small ammount for line friction. Generally you will need 5 to 10 pounds for most us sold drip systems.
There is a Canadian co that has a tube that operates under very small pressures. I may have it bookmarked in another computer. If so, I will post it later.

Benedita, There is a system that is used for indoor plant watering, I don't know why it wouldn't work for your application. You can water up to 10 plants with 1 system. You just need something to put your water in. It is called a Green Genius.

Here is a link that might be useful: Green Genius

When people go on vacation, there are several ways to deal with watering plants, like potted plants. You can place them in a pan of water, on top of a sponge (minus the individual water trays for the pots).

There are also things that fit on 2 liter bottles. You fill the bottle with water, tilt it upside down, and push the thing in the dirt. I think the cap is made out of ceramic so the water slowly seeps out over days or even a week. I've seen them at the store, don't know what they are called.

A new method is "water gel". It is a gel that slowly releases water. It is made out of vegetable oil. While it dissolves it releases water and leaves no residue. Pretty neat idea I thought.

Do you want temporary vacation watering, or fully automatic watering because you sometimes forget to water?

I have a southwest facing patio, and am growing many vegetable plants (peas, tomatoes, chard) that have low tolerance for drought. I am worried that only morning watering isn't going to provide enough water while I am at work all day and my veggie plants, out in the sweltering NYC heat of June-September, will be wilted by the time i get home.
I thought about the green genius, but I have plants with different water needs, so I was thinking about a simple adjustable drip system. 5 or 10 pounds of pressure if pretty small, right? a garden pond pump that can supply that right?
This is uncharted territory, I think.