indispensable is a strong adjective for something that you could not do without in English:

Water is indispensable to life.

Air as well as sunlight is, needless to say, indispensable to our daily life.

His long experience at the United Nations makes him indispensable to the talks.

In places where it snows a lot, kerosene is an indispensable item.

What is indispensable to our lives, along with food and clothes, is housing.

There is a good number of problems for which the Karush-Kuhn-Tucker conditions are insufficient to guarantee optimality, but this doesn't change the fact that these conditions are an indispensable tool for doing optimization.

Computer technology is indispensable to access many pertinent items of data.

These bodies have actually played indispensable roles in attaining these goals.

My uncle is a very heavy smoker; tobacco is indispensable to him.

Good knowledge of English is indispensable nowadays.

He was fully aware that he was an indispensable assistant

Edward was just telling us how indispensable you've become to him.

This is an indispensable step towards national reconciliation.