You want spot-free rinses so your paint dries with zero hard-water stains. The move is de-ionized (DI) water at the hose—softeners/inline carbon alone won’t get you truly spotless. Here’s the Amazon loadout that slaps:

Top picks (Amazon)

• CR Spotless DI-120 — the classic. True DI for glass-clear, air-dry finishes. Swap resin when TDS rises. 
  — Resin refills: CR Spotless R-120.  
• Unger Rinse ’n’ Go — compact DI canister that threads right to a garden hose. Great if you’re tight on space.  
• On The Go Portable Softener (16,000-grain) — pre-soften your city water to make your DI resin last way longer (softener first, DI last).  
• AquaticLife Spot-Free Car Rinse (Dual DI kit) — all-in-one DI kit with cartridges and fittings.  

What to avoid (if you want truly spotless)

• Basic “garden hose” carbon filters (Camco/Clear2O/AquaCrest, etc.) reduce chlorine/odors and some minerals, but do not hit zero-TDS. Fine for plants—not enough for spot-free drying on cars. If you try one, still finish with a DI rinse. (See Amazon categories for “spot-free rinse” showing DI units.)  

How to run it like a boss

1. Plumb order: Spigot ➝ (optional) softener ➝ DI unit ➝ hose/nozzle.
2. Wash with normal water, then flip to DI for the final rinse.
3. Air dry. No towels. No micro-marring. Just shine.

Quick links on Amazon (starter set)

• CR Spotless DI-120 (system)  
• Unger Rinse ’n’ Go (compact DI) + replacements  
• On The Go 16k-grain softener (pre-stage)  
• AquaticLife DI kit (all-in-one)  

If you want, tell me your water’s TDS (ppm) and I’ll spec resin usage + the most cost-efficient setup for your driveway. 🚿💦🚗💎