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 sizing right and you will spend less time and money on resin replacements while still getting a perfect 0 TDS rinse every time.
What the Tank Size Actually Means
When a DI tank is listed as “10L”, that refers to the resin capacity — it holds 10 litres of mixed-bed ion exchange resin. The tank itself is physically larger because it also needs space for water flow and the internal distribution system.
More resin means:
- More pure water before the resin needs replacing
- Longer intervals between refills
- Lower cost per wash over time
Less resin means:
- Lighter and more portable tank
- Lower upfront cost
- More frequent refills needed
Output by Tank Size
The table below shows real-world output based on input water TDS. These figures account for the natural efficiency curve of mixed-bed resin.
| Tank | Resin | Output at 50 ppm | Output at 100 ppm | Output at 200 ppm | Output at 300 ppm |
|---|---|---|---|---|---|
| Medium | 10L | 5,100-5,800L | 2,550-2,900L | 1,275-1,450L | 850-970L |
| Large | 15L | 8,000-9,000L | 4,000-4,500L | 2,000-2,250L | 1,330-1,500L |
| XL | 25L | 13,400-15,000L | 6,700-7,500L | 3,350-3,750L | 2,230-2,500L |
To find your input TDS: Use the TDS meter included with every Spot Free Rinse tank, or check the Water Spot Calculator for your city’s typical reading.
How Many Washes Per Resin Fill?
A standard car uses 25-35 litres of DI water per final rinse. Larger vehicles use more:
| Vehicle | DI Water Per Rinse | Medium 10L Washes* | Large 15L Washes* | XL 25L Washes* |
|---|---|---|---|---|
| Sedan / hatch | 25-30L | 85-116 | 133-180 | 220-300 |
| SUV / 4WD | 35-45L | 57-83 | 89-129 | 149-214 |
| Caravan | 40-60L | 43-73 | 67-113 | 112-188 |
| Boat (small-medium) | 30-50L | 51-97 | 80-150 | 134-250 |
| Windows (avg house) | 15-20L | 128-193 | 200-300 | 335-500 |
| Solar panels (10 panels) | 10-15L | 170-290 | 267-450 | 447-750 |
*Based on 100 ppm input water. Lower TDS = more washes; higher TDS = fewer washes.
Decision Guide by Use Case
You wash one car weekly
Recommended: Medium 10L — At 100 ppm input, you get 85-97 washes before a resin swap. That is nearly two years of weekly washes on a single fill. The Medium is the top seller for good reason: it balances capacity, portability, and cost.
You wash multiple vehicles or a car + caravan
Recommended: Large 15L or XL 25L — If you are routinely washing 2-3 vehicles per session, the extra resin capacity means fewer refills per year. The Large handles most multi-vehicle households. The XL is best if you also have a caravan, boat, or do commercial work.
You want something compact for travel
Recommended: Medium 10L — Compact enough for the boot, and delivers 85–97 car washes at 100 ppm. Perfect for weekend trips or caravan park use where you want spot-free results on the road.
You mainly clean windows or solar panels
Recommended: Medium 10L or Large 15L — Window and solar panel cleaning uses less water per session than car washing, so the resin lasts significantly longer. A Medium 10L can handle 150+ window cleans or 200+ solar panel sessions at 100 ppm.
You run a professional detailing business
Recommended: XL 25L — Maximum output between refills, lowest cost per litre. At 100 ppm input, you get 6,700-7,500 litres — enough for 220+ car rinses. The XL also handles higher-TDS water better because the larger resin bed maintains consistent output quality for longer.
Cost Per Wash Comparison
| Tank | Price | Resin Refill | Washes Per Fill* | Cost Per Wash (resin only) |
|---|---|---|---|---|
| Medium 10L | $499 | $159 | 90 | $1.77 |
| Large 15L | $649 | $225 | 140 | $1.61 |
| XL 25L | $999 | $349 | 235 | $1.49 |
*Average washes at 100 ppm for a standard car (30L/rinse).
Larger tanks have a lower cost per wash because resin scales efficiently — double the resin gives you more than double the output due to better exchange efficiency in a larger bed.
What Is Included With Every Tank
Every Spot Free Rinse tank ships ready to use:
- Pre-filled tank with premium high-flow mixed-bed resin
- Protective tank jacket (black or navy blue)
- Male hose connectors and approximately 2 metres of hose
- External bypass valve (Medium, Large, XL)
- Complimentary TDS meter
- Printed instructions
All tanks connect to standard Australian garden hose fittings. Compatible with garden hoses and pressure washers — full pressure, no flow restriction.
Still Not Sure?
Start with the Medium 10L. It is the right size for the majority of Australian households — one or two vehicles washed weekly, with enough capacity to handle the occasional caravan or boat rinse. If your water is particularly hard (250+ ppm), or you wash more than three vehicles regularly, step up to the Large 15L or XL 25L.
