  A search for inverse beta decay electron antineutrinos has been carried out
using the 825 days sample of solar data obtained at SK. The absence of a
significant signal, that is, contributions to the total SK background and their
angular variations has set upper bounds on a) the absolute flux of solar
antineutrinos originated from ${}^8 B$ neutrinos $\Phi_{\bar{\nu}}({}^8 B)=<
1.8\times 10^5 cm^{-2} s^{-1}$ which is equivalent to an averaged conversion
probability bound of P<3.5% (SSM-BP98 model) and b) their differential energy
spectrum, the conversion probability is smaller than 8% for all $E_{e,vis}>6.5$
MeV going down the 5% level above $E_{e,vis}\approx 10$ MeV. It is shown that
an antineutrino flux would have the net effect of enhancing the SK signal at
{\em hep} neutrino energies. The magnitude of this enhancement would highly
depend on the, otherwise rather uncertain, steepness of the solar neutrino
spectrum at these energies.
