Choosing a DI water tank comes down to three things: how hard your water is, what you are washing, and how often you wash. Get the size right and you change resin less often while still getting a 0 ppm rinse every time.
Not sure how hard your water is? Look up your suburb in our Australian tap water TDS guide, which covers 278 cities, towns and suburbs using each water provider's own figures.
What the Tank Size Actually Means
When a DI tank is listed as "10L", that is the resin capacity: it holds 10 litres of mixed-bed ion exchange resin. The tank itself is bigger, because it also needs room for the water to flow through the resin.
More resin means more pure water before a replacement, and fewer resin changes a year. Less resin means a lighter, cheaper tank that needs changing more often. Output scales directly with the amount of resin: a 15L tank makes one and a half times what a 10L tank makes from the same water.
Output by Tank Size
How much 0 ppm water you get depends on your tap water TDS. These figures are for fresh resin.
| Tank | At 50 ppm | At 100 ppm | At 200 ppm | At 300 ppm |
|---|---|---|---|---|
| Medium 10L | 5,100 to 5,800L | 2,550 to 2,900L | 1,275 to 1,450L | 850 to 970L |
| Large 15L | 7,650 to 8,700L | 3,825 to 4,350L | 1,910 to 2,180L | 1,275 to 1,450L |
| XL 25L (special order) | 12,750 to 14,500L | 6,375 to 7,250L | 3,190 to 3,630L | 2,130 to 2,420L |
To find your TDS: use the TDS meter that comes with every Spot Free Rinse tank, check your suburb in the tap water TDS guide, or use the Water Spot Calculator.
How Long Does a Fill Last?
A car takes about 25 to 35 litres for the final rinse, a 4WD or SUV a little more, and a caravan around 40 to 60 litres. Here is roughly how long a fresh fill lasts if you rinse one car every week:
| Tank | Soft water, 100 ppm | Moderate, 200 ppm | Hard, 300 ppm |
|---|---|---|---|
| Medium 10L | About 20 months | About 10 months | About 6 to 7 months |
| Large 15L | About 2.5 years | About 15 months | About 10 months |
Wash every fortnight and those times roughly double. Wash two cars a week and they halve. Treat these as a guide rather than a promise: resin also ages once it has been wet, so a tank that sits for months between washes will not quite reach these figures. The TDS meter is what tells you when it is actually time. For more detail, see our resin life guide.
Which Size Suits You?
You wash one or two cars at home
Medium 10L. It suits most Australian households, stores easily and fits in the boot for trips away. It is our most popular tank for good reason.
You wash several vehicles, or a car and a caravan
Large 15L. The extra resin means fewer changes a year, which matters once you are rinsing two or three vehicles at a time or a whole van.
Your water is hard, or you are on bore water
Large 15L. Hard water uses resin faster, so the bigger bed saves you changing it as often. If your water is well above 400 ppm, have a read of our bore water guide and our RO/DI vs DI comparison first.
You mainly clean windows or solar panels
Medium 10L or Large 15L. A house of windows or a solar array uses less water per session than a car, so the resin goes a long way. See our guide to window cleaning equipment for the pole setup.
You run a detailing or cleaning business
Large 15L, or the XL 25L by special order. At commercial volumes the biggest resin bed means the fewest stops. Get in touch if you want to talk through the XL.
What Is in the Box
Every Spot Free Rinse tank is assembled and tested in Brisbane and ships ready to use:
- DI tank, pre-filled with mixed-bed resin and pre-assembled
- Bypass tank head, so you can switch between tap water and pure water
- TDS meter
- 2 metres of hose
- Written instructions and a video guide
All tanks use standard Australian garden hose fittings and need no power or pump.
Still Not Sure?
Start with the Medium 10L. It is the right size for most Australian households washing a car or two, with room for the occasional caravan or boat. If your water is hard (250 ppm and up) or you regularly wash three or more vehicles, step up to the Large 15L.
Still weighing up tanks against cartridges and other systems? Our guide to the best DI water systems for car washing in Australia compares every type side by side.
Frequently Asked Questions
What size DI tank do I need for one car?
The Medium 10L suits most people washing one or two cars. Step up to the Large 15L if your water is hard or you wash several vehicles.
Does a bigger tank give better water?
No. Every tank gives 0 ppm water while the resin is fresh. A bigger tank simply makes more of it before the resin needs replacing.
How do I know when the resin needs replacing?
Check the output with the TDS meter. When it climbs above about 10 ppm, or you notice very light spotting, it is time to replace the resin.
