'Eternity' in the Bible

But whoever drinks of this water which I will give to him will never be thirsty for eternity, but the water which I will give to him will become in him a well of water springing up to eternal life."

The Jews said to Him, “Now we know that You have a demon [and are under its power]. Abraham died, and also the prophets; yet You say, ‘If anyone keeps My word, he will never, ever taste of death.’

And I give them eternal life, and they will never, ever [by any means] perish; and no one will ever snatch them out of My hand.