As long as the water was sterile it is completely fine. You can even use distilled water for eluting from the columns but yields are slightly lower due to the pH being not ideal.

You just need to assume that the concentration is lower by how much you diluted it with the water. Use a pipette to find out the new volume and calculate the concentration difference based on the original volume.

I eluted my plasmid in TE because I needed to use the plasmid for transfection next week. Is it still ok to consider this plasmid? Is using TE and water both at the same time okay?

I just checked it was 400ul (with TE) earlier and after the spillage it was 442 ul (with 42ul of water spillage)

Tris/EDTA buffer is only really needed for long term storage. The tris is a buffer to keep the pH basic to avoid acid catalyzed cleavage of nucleotide backbones while the EDTA is to remove free metal ions which also catalyze DNA degradation. The EDTA also aids transfection by impairing cell adhesion so a larger surface area is exposed for transfection. Tris on the other hand can be detrimental to transfection as it can interfere with particle sizes formed by the transfection reagents. Assume your DNA concentration is now 1,778ng/ul. The water will not prevent transfection and at most will just alter transfection efficiency so you should be ok to use your plasmid.

Thank you Robert Adolf Brinzer sir for your valuable response.