P.4 English --- about 'the'

yovin

P4 English
1.She used magazine paper to wrap the presents.  OR  She used magazine paper to wrap presents.
2.She used old towels to clean the floor.  OR  She used old towels to clean floor.
3.You should not waste the water.  OR You should not waste water.

My answers: 1,2 with the  3 without the.
But the answers are both to use the.

My son ask ' 如果在不指定的情況下是不應用THE , 那麼不指定的任何presents 及floor, 也不應用THE.   Why all the answers use the? '

我不懂答, 是否用與不用也可以? Please help me and save me.
Thanh you.