Ironically, pinholes in grout is caused by too much water in the grout mix. Once the water is dried or evaporated, it leaves behind tiny pockets. Thankfully, in order to fix this issue, you do not need to rip out the old grout.

Why am I getting holes in my grout?

Pinholes in grout are caused by the installer's use of soupy grout. Too much water was used during mixing or the installer left too much water on the joints while wiping. As the grout dried, the water evaporated, leaving holes.

How do you know if grout is leaking?

If your grout is visibly cracked or crumbling, it's likely going to be letting water behind your tiles. Even if your grout doesn't appear to be damaged, if it's not water-resistant it could potentially be the source of the leak.