This is the 200th most frequent Portuguese word.
falta
"Lack," "absence," or "fault."
Here, "falta" refers to the absence or shortage of something, in this case, water.
A falta de água está preocupante.
The lack of water is worrisome.
In this sentence, "faltam" (the form of "falta") is used to express that a certain amount of time is remaining.
Faltam apenas dois dias para o evento.
There are only two days left until the event.
Here, "falta" is used in the expression "sentir falta" which means 'to miss someone or something.'