I don't really see the benefit of sterile water, but you may.
To quote from the Fermentis data sheets "Pitching instructions: Re-hydrate the dry yeast into yeast cream in a stirred vessel prior to pitching. Sprinkle the dry yeast in 10 times its own weight of sterile
water or wort at 23C ± 3C."
and to clarify why, I clearly see benefit from using Sterile Water, It is to prevent
the contamination vector that is present in non steralized water. I believe that
non sterile water Is probably fairly high in contaminants that could be very
detrimental to brewing.
Also, in washing yeast as from a yeast cake, it just offers a media for washing that is devoid of worries.