Why Feeding Tap Water Through a DI Tank into a Pressure Washer Is a Bad Idea

Why We Don’t Recommend Using a DI Tank with a Pressure Cleaner for Car Detailing

When detailing a car, getting that spotless, streak-free finish is all about using pure water—water free from minerals and impurities that cause water spots. DI (Deionisation) tanks are a popular way to produce pure water on demand, and many detailers know this.

But here’s where a common mistake happens:

Some people try to feed tap water through a DI tank straight into a pressure cleaner to rinse a car. We strongly recommend against this setup. Here's why.

The Problem with Tap → DI Tank → Pressure Cleaner

Let’s break down why this setup doesn’t work well and can end up costing you more time and money.

1. High Flow Rates = Poor Filtration

DI tanks are designed for low-pressure, low-flow applications, like water straight from your tap into a hose or spray gun. When you connect a pressure washer, the high flow rate pulls water through the DI tank too quickly, not giving the resin enough contact time to effectively purify the water.

The result? The water isn’t truly pure, and you still get spotting—defeating the purpose of using a DI tank in the first place.

2. You’ll Waste DI Resin – Fast

Because water is rushing through the DI tank, the resin inside works overtime and gets used up much faster than normal. Instead of lasting weeks or months, your resin could be depleted in just a few uses. Resin isn’t cheap, so this setup becomes a very expensive way to get mediocre results.

3. Pressure Cleaners Can Contaminate the Water

Pressure washers, especially older or lower-quality models, can sometimes introduce oil, metal particles, or other contaminants into the water stream from internal components. This can undo the benefits of pure water and leave unexpected marks or streaks on your car’s surface—even if you’re using DI water.

A Better Way to Use DI Water for Spot-Free Rinsing

Option 1: Use DI Water at Tap Pressure

For the final rinse in car detailing, you don’t need high pressure. In fact, high pressure isn’t ideal for this step. Using pure DI water at regular tap pressure with a trigger spray gun or nozzle is more than enough to rinse your car and achieve a spotless, streak-free shine.

This method is simple, cost-effective, and safe for your DI tank and resin.

Option 2: Buffer Tank Setup for Pressure Washers

If you really want to use your pressure washer for a pure water rinse, here’s the correct method:

1. Fill a buffer tank with purified water from your DI tank at normal flow rate.
2. Feed your pressure washer from the buffer tank.

This setup ensures the DI resin is used efficiently, water is fully purified, and your pressure washer won’t damage the DI system or compromise water quality.

Summary: Protect Your DI Tank, Save Resin, Get Better Results

Feeding water directly from the tap → DI tank → pressure cleaner is inefficient, costly, and ineffective. You’ll waste resin, risk poor purification, and potentially contaminate your water stream.

Better alternatives:

• Tap → DI tank → spray gun = simple, spot-free rinse.
• Tap → DI tank → buffer tank → pressure washer = safe high-pressure option.