I have not heard of the White's PI 2000. I did an internet search for that term on Google and nothing came up either.
I had a White's PI machine back in the 1990's and it was o.k. I once used nothing but White's detectors and they still have some of the best machines around but if I were you, and you are good with a PI machine, I would go with a Garrett or Tesoro PI. Garrett makes a great mid level machine called the Sea Hunter which has discrimination capability. Check out the reviews for it and you will see that it is really good. If you want to go high end, check the Infinium. It is like the Sea Hunter on Steroids. Tesoro has some great machines also in the Sand Shark and Tiger Shark. Minelab doesn't offer any mid range water machines but the Excalibur is an awesome VLF water detector too.
So many detectors, so little time! Good Luck.
Jim