Regamos con la manguera a falta de depósito de agua.

A falta de is a fixed expression meaning for lack of, in the absence of, or since there isn’t / we don’t have.

In this sentence, it explains the reason or circumstance:

• a falta de depósito de agua = because there is no water tank / in the absence of a water tank

It is not usually translated word for word.

Because Spanish often leaves out subject pronouns when the verb already shows who is doing the action.

• Regamos already means we water or we watered
• So nosotros regamos is possible, but usually unnecessary

You would add nosotros only for emphasis, contrast, or clarity.

It can mean either one.

Regamos is ambiguous because it is both:

• present tense: we water
• preterite: we watered

Only the context tells you which meaning is intended. In an isolated sentence like this, learners often interpret it as present, especially if it describes a general practice or current situation.

Con is used to express the instrument or tool used to do something.

So:

• regar con la manguera = to water with the hose

This is very common in Spanish:

• escribir con un bolígrafo = to write with a pen
• cortar con un cuchillo = to cut with a knife

Using la manguera suggests a specific or understood hose:

• the hose we have
• the hose being discussed
• the usual hose used for watering

Spanish often uses the definite article where English might be more flexible.

If you said una manguera, it would sound more like a hose, not a specific known one.

Yes, the direct object is omitted, and that is very normal in Spanish if it is obvious from context.

For example, the full idea could be:

• Regamos el jardín con la manguera...
• Regamos las plantas con la manguera...

If everyone already knows what is being watered, Spanish often leaves it out.

Here depósito de agua means water tank, water storage tank, or sometimes cistern/reservoir, depending on context.

A learner should be careful not to assume depósito means only the English word deposit. In Spanish, depósito has several meanings, and in this phrase it clearly refers to a container or storage system for water.

Good question. A falta de depósito de agua is a compact, somewhat condensed way of speaking. It treats depósito de agua as a general category rather than one specific tank.

However, many speakers would also say, and some might even find more natural:

• a falta de un depósito de agua
• como no tenemos un depósito de agua
• al no tener depósito de agua

So the version without an article is possible, but it sounds a bit more compressed, formal, or technical.

Sometimes yes, but the nuance is slightly different.

• por falta de = because of lack of
• a falta de = in the absence of / for lack of / since there isn’t

In many contexts they are close, but a falta de often suggests a workaround or substitute situation:

• A falta de depósito de agua, regamos con la manguera
  = Since we don’t have a water tank, we use the hose

That nuance fits this sentence well.

Yes, it is understandable, but it sounds somewhat condensed and slightly formal or technical.

More everyday alternatives might be:

• Como no tenemos depósito de agua, regamos con la manguera.
• A falta de un depósito de agua, regamos con la manguera.
• Al no tener depósito de agua, regamos con la manguera.

Also, many speakers might place the reason first:

• A falta de depósito de agua, regamos con la manguera.

That word order can sound a bit smoother.

Regar is the normal everyday verb for to water plants, gardens, lawns, etc.

• regar las plantas
• regar el jardín

Irrigar exists, but it is usually more technical, agricultural, medical, or formal. So for ordinary speech, regar is the natural choice here.