The Answer;
In the name of Allah, Most Gracious, Most Merciful.
If you are not in wudu and your hand, fingertip, fingernail, toenail or any other part of your body (that must be washed during wudu) comes into contact with water covering less than the surface area of 25 square yards or 225 square feet, (for example, water in a bucket or tub) that water will become Musta’mal (used), and it can no longer be used for wudu or ghusl (ogligatory bath), regardless of whether this was done deliberately or unintentionally. Similarly, if ghusl is due and any unwashed part of the body comes into contact with water, this water cannot be used for wudu or ghusl.
However, it doesn’t matter if a washed hand or washed part of the body comes into contact with the water, the water will remain unused. (Bahar-e-Shari’at, pp. 333, vol. 1)
And Allah(swt) alone knows best.