Fornander:

"KOI, v. Haw., to flow, rush, like water over a dam; koi-ei-ei, a rapid current; koi-ele, to overflow.

N. Zeal., toi, to dip in water, to duck.

Iaw., toya, water.

Sanskr., toya, water. Apparently there is no etymon for this word in Sanskrit or Vedic, for Benfey suggests that it derives 'perhaps from tu.' But the primary, at least the Vedic, meaning of tu is 'to be all-powerful'. Taking the New Zealand term as the best-preserved among the Polynesian dialects, it certainly offers a better etymon to the Sanskrit toya than the Vedic tu."