Washing Cars in Direct Sun Without Water Spots

Take your car detailing to the next level with expert tips from Wilson Auto! Learn how to wash your car in direct sun without water spots.


If you want to skip the details and get the summary, jump down to the BIG IDEAS.


DI tanks (deionized water tanks) are some of the most helpful tools for detailers because they basically take the hard work out of car washing… 

You can use DI water to eliminate your need to dry another car & completely avoid water spots

What is a DI tank?

A DI tank is nothing more than a container that holds resin (a sandy/bead-like substance) that filters the hard water coming out of your tap. It turns your hard water into soft water so that you don’t worry about water spots when you are washing.

What are water spots?

When you wash your car, and the water dries on the paint, you are sometimes left with tiny spots that make your car look terrible:

These spots are just leftover solids that were in the water you used. When the water evaporated, the solids were left behind.

As a detailer, you probably already feel like you need a DI tank so that you don’t have to worry about water spots because well…

They SUCK!

That said, let’s talk about avoiding water spots WITH a DI tank, WITHOUT a DI tank, and even FIXING water spots when they happen:

When Should I Buy a DI Tank?

When you are washing so many cars in the direct sun that you can no longer take how much it’s slowing you down. Here’s how I think about it: I used to go to a gym where there was no child care available… that meant that when I was working out, my wife had to watch our daughter. Well, when we only had 1 daughter, that was no big deal, but since we had TWINS after our daughter, I can no longer go to the gym with no childcare because my wife can’t take care of our 3 kids alone while I am working out. So I now pay MORE money for a gym with child care.

This is exactly how I would think about the “right” time to get a DI tank. I washed cars in the direct sun for about 3 years before I finally said: “I am seeing SO MANY cars now, and wasting SO MUCH TIME doing things the long way to avoid water spots that it is no longer working. I now have to invest some money so I can get the proper tools for the next level. 

If several hundred dollars is a big investment for your business right now, and you aren’t ALWAYS washing in direct sun… you may want to hold off until it’s necessary.

WHICH DI tank should I buy?

The number 1 thing that separates DI tanks is SIZE. Understand that a DI tank is generally not “good or bad” like other tools in detailing. A DI tank is only as good as the water you are using and the size of the tank… here’s what I mean:

The DI tank is filled with a resin that essentially filters the water. Well, filters eventually have to be replaced, and the dirtier the water, the more often you have to replace them. The same is true here. If your water is REALLY HARD, you may have to replace the resin more often, but generally speaking, there isn’t really “good resin & bad resin.” The larger the tank and the cleaner the water, the less you will have to replace it. The smaller the tank and dirtier the water, the more you will have to replace it.

Here’s the simple way to make a purchase decision here:

How much portability do you need with your DI tank? Are you going to be moving it a lot? Is it going to sit in the same place all the time? 

Here are some more portable options I suggest for the mobile detailers:

Adams DI Tank

On The Go Portable Tank

DI Rinse Pro 50 System (This is the smaller version of what I use professionally)

The million-dollar question here is: How often will I have to change out the resin if I buy one of these smaller tanks?

The problem is… it depends. The hardness of your water and the frequency with which you use the system will determine the answer. I am running experiments with this to give you a PROPER answer… but only time helps here.

Here are some larger options for stationary detailers:

Pro 100 DI Rinse System (This is what I use professionally)

CR Spotless Water System (popular in the detailing world)

Why pick one over the other? For most, it just comes down to price and build quality, NOT how many washes you will get out of one or the other.

Let’s talk about how to avoid water spots WITH NO DI TANK:

  1. Rinseless washing. One gallon of distilled water and a couple of cap fulls of Optimum No Rinse make for a powerful way to wash a car with distilled water and minimize your work. Here’s a full video explanation.
  2. Sometimes a car is SO DIRTY that a rinseless wash method doesn’t make sense simply because you can’t introduce enough water. So how do you wash in the traditional way & avoid water spots?
    • The product Formula 4 Spray Wax is a rinsing aid that, when used with your final rinse, will actually cause the hard water on the paint to bead up and roll off, giving you more time to rinse and dry the car before any water spots can form. This is the most effective way to wash in direct sun without a DI tank and avoid water spots. Here’s a full video explanation.
    • There is a comparable product called “EZ beads” from Auto Magic that serves the same purpose. It’s helpful to look at both of these products to get a full understanding of what they do and why they are so helpful. Here’s a full video explanation.

The products I listed above are actually found in the industrial car wash industry, but I adopted them as a detailer because they are so effective in this application.


A DI tank is the easiest and most effective way to avoid water spots & wash cars in the direct sun. With a DI tank, you don’t even have to dry the car. I use a DI tank called the Pro 100 from “Spot Free Water Systems.” Understand that there’s really nothing special about different branded DI tanks other than the amount of resin that they hold. The more resin they hold, the longer it will give you spot-free water before you have to change the resin inside. 

  1. When should you buy a DI tank? When you’re washing so many cars in the hot sun that it is noticeably slowing you down. Here’s how I thought about it BEFORE I had one: “Yes, it’s frustrating NOT to have a DI tank, but I’m not washing enough in the direct sun to justify a $625 purchase right now, and I can avoid water spots using certain chemicals right now, so even though it takes a little bit longer it’s worth it to wait.”

  2. Which DI tank should you buy? The Pro 100 that I use seems to last a long time before needing to replace the resin. Let’s say 30-50 washes (depending on your water). This is also affected by how HARD your water is. Remember, the big difference between DI tanks is size, so that is what I would focus on when making a purchase decision. If you are mobile, something smaller is convenient; if you are stationary, you can get something larger.

As a detailer myself… I hate water spots just as much as you, so I hope this helps.