Stokk Reverse Osmosis System S1 (8 Stage, 400 GPD, Tankless)

What contaminants does the 8-stage filtration remove?

The system removes over 1000 contaminants including PFAS, microplastics, bacteria, viruses, heavy metals like lead and mercury, chlorine, fluoride, nitrates and total dissolved solids. The 0.0001μm reverse osmosis membrane blocks particles down to molecular level. SGS certification confirms effectiveness against NSF/ANSI 58 & 42 standards, ensuring removal of both aesthetic impurities and health-related contaminants regulated by EPA.

How much space does the tankless design actually save?

The tankless design saves over 75% of under-sink space compared to traditional RO systems with storage tanks. Measuring just 37cm x 11.4cm x 30.4cm, it fits in tight spaces where tank-based systems cannot. Traditional systems require a 40-50cm diameter tank plus the filtration unit, whilst this system eliminates the tank entirely. The compact footprint leaves room for other under-sink storage needs.

What is the actual water flow rate and how long does it take to fill containers?

The system produces 400 gallons per day with a maximum flow rate of 0.28 gallons per minute. It fills one cup (250ml) in approximately 10 seconds. A 1-litre bottle takes about 40 seconds, whilst a gallon jug requires roughly 4 minutes. Flow rate is slower than tap water but faster than many RO systems. For best results, let water run for 30-60 seconds initially to achieve optimal TDS levels.

How often do filters need replacement and what's the cost?

The PPC (pre and post carbon) filter typically lasts 12 months with average family use, whilst the RO membrane can last 12-24 months depending on water quality and usage. Filter replacement uses a twist-and-pull design taking just 2 seconds. The system includes a built-in filter life reminder to track replacement timing. Replacement filters are available through Stokk, though some users report difficulty finding PPC filters in stock.

Does installation require professional help or special tools?

Installation takes approximately 30 minutes and requires basic DIY skills. You'll need a power drill with 1/4" bit, Phillips screwdriver and kitchen shears for tube trimming. The system requires an electrical outlet under the sink and drilling holes for the faucet and drain connection. All necessary components are included except tools. The creative tube connection system makes installation straightforward for most homeowners.

What electrical requirements does the system have?

The system requires a standard electrical outlet under the sink for the automatic flushing and control functions. If no outlet exists under your sink, you'll need to install one or drill a hole to access a nearby outlet. The system is corded electric and FCC certified for safety. Power consumption is minimal, primarily used for the automatic flushing cycle and filter life monitoring.

How does the 2:1 pure to drain ratio compare to other systems?

The 2:1 ratio means for every 3 gallons of input water, you get 2 gallons of pure water and 1 gallon goes to drain. This represents 800% better water efficiency than traditional under-sink RO systems, which typically operate at 1:3 or 1:4 ratios. The improved efficiency reduces water waste significantly whilst maintaining optimal membrane performance and extending filter life.

Why does water quality vary when first turning on the system?

When the system sits unused, water equalises across the membrane, causing TDS levels to rise temporarily. Running water for 30-60 seconds flushes the system and achieves optimal filtration performance, typically reducing TDS to 8-12 ppm from input levels of 160+ ppm. This is normal behaviour for tankless RO systems. For consistent quality, consider filling containers for refrigerator storage rather than drawing water on demand.