Rainwater for your toilets, washing machine and outdoor taps
The Carat AA Silentio system collects the rain that falls on your roof, stores it in an underground tank and supplies it on demand to your toilets, washing machine and outdoor taps. It’s a complete package for homeowners, self-builders and installers: tank, filter, floating intake and pump unit, chosen to work together.
How it works
Rain runs from your downpipes into one pipe and into the tank. On the way in, it passes through an Optimax filter that keeps leaves and debris out, and a jet wash feature periodically rinses debris off the filter. Inside the tank, a floating intake draws water from just below the surface, where it is cleanest.
The AA Silentio pump unit is wall-mounted inside the property, for example in a plant room or garage. When you flush a toilet or open a tap, the pump draws rainwater from the tank and supplies it under pressure. Because the pump sits above ground rather than in the tank, it’s easy to reach for servicing. A reversible flow filter in the package adds another stage of filtration, and a water level sensor in the tank gives an accurate reading of how much rainwater is left. The pump has dry-run protection.
Automatic mains backup that keeps the tank for rainwater
The AA Silentio unit has its own mains water cistern. When rainwater in the tank runs low, the system draws from this cistern instead, so your toilets and washing machine keep working. Mains water never goes into the underground tank, so the whole tank stays available for rainwater. A float sensor on the unit makes sure the house is always supplied, using only the mains water it needs.
What the AA air gap does
UK water regulations require a physical break between harvested rainwater and the mains supply. The AA Silentio unit has an AA air gap (Family A, Type A, to BS EN 13076): the mains water drops into the cistern through open air, so rainwater can never flow back into the mains pipe. Read more: What is an AA air gap in a rainwater harvesting system?
AA Silentio or AA Eco-Plus?
Both systems use the same tank, indoor pump unit, mains backup cistern and AA air gap. The AA Silentio package adds a reversible flow filter, a water level sensor in the tank and a jet wash feature for the tank filter. Compare them in our guide: AA Eco-Plus vs AA Silentio: which rainwater harvesting system is right for you?
Choose your size
The Carat is an upright underground tank. It takes up less ground area than a shallow-dig Platin tank of similar capacity, but needs a deeper hole. The Carat tank is made from 100% recycled plastic and is installed with gravel backfill rather than concrete, which makes installation simpler and saves around £60 per cubic metre. Carat tanks are trusted across Europe for their reliability in rainwater harvesting.
| Capacity | Length | Width | Total height (with Maxi dome) | Weight |
|---|---|---|---|---|
| 2,700 litres | 2,080mm | 1,565mm | 2,010mm | 120kg |
| 3,750 litres | 2,280mm | 1,755mm | 2,200mm | 150kg |
| 4,800 litres | 2,280mm | 1,985mm | 2,430mm | 185kg |
| 6,500 litres | 2,390mm | 2,190mm | 2,710mm | 220kg |
All sizes have an 800mm tank dome. The tank body is 1,400–2,100mm tall and the Maxi dome adds 610mm. Choose a pedestrian lid for lawns and garden areas, or a vehicle lid if the tank will go under a driveway.
Useful links
- Prefer the simpler package? See the Carat AA Eco-Plus system
- Need a shallower dig? See the Platin AA Silentio system (1,500–7,500 litres)
- Tank going in deeper? Add an Extension Piece
- See how the system fits together: How rainwater harvesting systems work: the AA system explained
- Not sure which system you need? Read our guide: Comparing rainwater harvesting systems: direct, indirect and garden-only
- Work out the right tank size with our rainwater harvesting tank size calculator
Images are for illustration; components may be upgraded or replaced with equivalent alternatives.
