Quick answer: Membrane Solutions sells the water problem, and the honest rule is buy for the job, not the micron number on the box. The UV countertop gravity system ($179.99)
Quick answer: Waterdrop's lineup sorts by what's actually in your water — so test first. The G3P800 tankless RO ($849.00) is the quantified contaminant killer: Phoenix tap at 400–600 TDS
Quick answer: with filters, the part number is the product — match the label inside your appliance, then argue about price. The LT1000PC three-pack ($29.99) and the Samsung DA97-17376B three-pack