You're missing the point! The original Tap Water Filter had specialized resins and produced DI (De-ionized) water (that also had nitrates removed)...but the cartridge use life wasn't that good, at least with my water. I can't speak to why API discontinued production/marketing of the product. Could be low sales, not enough profitability - who knows.
After discussions with MARS Tech Support, I took a spent cartridge and emptied the resin, then filled the cartridge with new API Nitra-Zorb (a totally different resin that adsorbs nitrates). The filter connects to a faucet and water is trickled through it to produce water that has zero nitrates! (This is a DIY Pozzani filter). The real beauty is that the resin recharges over and over with regular salt water.
So no, it can't be good....it's GREAT.