Why Does the HydroSpark+ Have a Divider in the Tank?

If you've looked inside your HydroSpark+ water tank, you've probably noticed a small divider on one side. The larger side holds about 3 litres. The smaller side holds about 1 litre. And when you fill the tank to the MAX line, the total amount of water is about 5 litres, and the water sits well above the divider — making it look like the divider does nothing at all.

So what's it for?

A Quick Primer on How RO Filtration Works

Reverse osmosis works by pushing water through an extremely fine membrane (0.0001 µm). Pure water passes through. Dissolved solids, heavy metals, and other impurities get left behind.

But here's the thing most people don't realise: RO filtration is not efficient by nature. In a traditional system connected to your plumbing, for every 1 litre of clean water produced, 3 to 4 litres of water are flushed down the drain as waste. That's a lot of water thrown away.

To put that in perspective: if the HydroSpark+ is used in the piped water mode (as opposed to using the tank), filling the tank to the MAX line (5 litres) would yield just 1 litre of purified water. The other 4 litres would go straight down the drain.

How the HydroSpark+ Solves This

The HydroSpark+ is a countertop system. In storage tank mode, there's no drain connection — so where does the residual water go?

It goes back into the tank.

When the system filters water, two things happen at once:

1. Clean water is dispensed from the spout.
2. Residual water — what didn't pass through the membrane — is returned to the smaller side of the tank.

The residual water re-enters at the base of the smaller compartment. Since the water level starts above the divider, both sides of the tank are one connected body of water — so it simply mixes back in. The system then draws from this pool again, filters again, dispenses again, and returns residual water again.

This is called recirculation, and it's how your HydroSpark+ achieves a much better ratio of clean water to residual water — roughly 4 litres of clean water for every 1 litre of residual, instead of the 1:4 ratio of traditional systems. That's a 16× improvement in water efficiency.

If this sounds like the system is filtering increasingly "dirtier" water, remember — the RO membrane filters to 0.0001 µm precision on every single pass. It doesn't matter whether the source water is fresh from the tap or on its third trip through the tank — what comes out of the membrane is purified each time. Recirculation simply means less water is thrown away, not that the water you drink is any less pure.

So When Does the Divider Actually Matter?

As you keep dispensing water, the level in the tank drops. Eventually, it reaches the top of the divider.

At this point, the two sides of the tank separate. But the smaller side is already full to the brim of the divider — and the system keeps returning residual water to it through the valve at the base. Since it's already full, new residual water displaces the cleaner water sitting above it, making it overflow back into the main tank. Recirculation continues, but the main side keeps dropping because clean water is being dispensed out faster than residual water is being returned.

When the main side runs empty, the system stops and tells you it's time to refill.

This is where the divider earns its keep. That 1 litre sitting in the smaller compartment is the most concentrated residual water from your entire filtration cycle. The system can't accidentally draw from it, and you know exactly what to pour away.

What to Do When It's Time to Refill

1. Lift out the water tank.
2. Pour away the remaining water (this is the residual water in the smaller compartment).
3. Refill the entire tank with fresh tap water to the MAX line.
4. Place it back in the unit.

That's it. No buttons to press, no readings to interpret. The design handles it for you.

Why a Divider Instead of a Sensor?

You might wonder: couldn't the system just use a water quality sensor to tell you when to change the water?

The HydroSpark+ does have a TDS (Total Dissolved Solids) sensor built in — you can check your water quality readings anytime from the settings screen. But the system doesn't rely on it to decide when you should flush and refill. Sensors can drift over time, need calibration, and depend on firmware logic to interpret readings correctly. A physical divider doesn't fail; it enforces a fixed, membrane-friendly 4:1 recovery ratio every single time, regardless of your tap water quality.

It's a deliberately simple solution to a complex problem — and it means your RO membrane lasts longer because it's never forced to filter water that's been through too many cycles.

The Short Version

Phase	What's happening
Tank full (above divider)	One body of water. System filters, dispenses clean water, returns residual water at the base of the smaller compartment — it all mixes freely.
Water drops to divider	Residual side is full and stays full — new residual water overflows back into the main side. Main side keeps dropping as clean water is dispensed out.
Main side empty	System stops and prompts you to refill. Pour away the remaining ~1L of residual water, refill with fresh tap water.

The divider is a simple construction that does a surprisingly important job — it makes sure you always discard the right amount of residual water, protects your filter membrane, and keeps things simple.