It is normal spider housekeeping
Tarantulas move substrate constantly. A water dish may sit exactly where the spider wants to dig, dump excavated soil or extend a webbed retreat. The behaviour is frustrating but usually not a sign that anything is wrong.
Refill rather than argue
Remove enough substrate to expose the dish, rinse if needed and refill it. Repeatedly relocating the dish can simply move the conflict to another corner.
Why the water disappears
Dry substrate can wick water out of a buried dish quickly. If that happens, clear the rim so the water remains available rather than assuming the spider no longer needs a dish.
Do not punish normal digging
Avoid destroying a burrow or web just to keep the enclosure tidy. The spider's landscaping priorities are more important than the keeper's visual preferences.
Try another position if necessary
If one location is buried every day, moving the dish a short distance can help, especially if the original spot has become part of the burrow entrance.
Keep perspective
A tarantula filling its bowl with dirt is one of the most ordinary keeper annoyances in the hobby. Clean water access matters; a perfectly tidy enclosure does not.