Rainwater Unit Sigma

  • Compact and economical
  • Self-priming suction pump in wall unit for pumping water from rainwater storage tank to appliances
  • Mains water top-up in the integral top-up tank
  • ZETA 02 pump controller:
    Less than 0.2 watts in standby mode


Design and area of application

The SIGMA rainwater unit is designed for use in single-family homes. Virtually all its components are integrated into a single housing. These include the energy-efficient ZETA 02 pump controller, the self-priming suction pump and the mains water top-up equipment. Thanks to its compact dimensions, the SIGMA rainwater unit is particularly easy to install and is typically sited in the utility room or cellar. The integral pressure indicator displays the pressure in the rainwater supply circuit.

Operating principle

The SIGMA rainwater unit sucks rainwater out of the storage tank and feeds it under pressure into the rainwater supply circuit. When all extraction points are closed, the pump in the SIGMA unit switches off after a brief delay. If one extraction point is opened or the toilet is flushed, the controller detects the pressure drop and restarts the pump immediately. As soon as all extraction points are closed again, the system pressure increases and the pump shuts down automatically.

Self-priming suction pump

The SIGMA rainwater unit is equipped with a self-priming suction pump. This device sucks water out of the storage tank and pumps it under pressure to the valves at the appliances. The SIGMA rainwater unit is capable of pumping up to 66 l/min. The maximum delivery head is 34 m (Sigma 3 model) or 45 m (Sigma 4 model).

Uninterrupted water supply

If the rainwater in the storage tank runs out during a prolonged dry spell, the system switches automatically to mains water operation. The low water level in the rainwater tank is sensed by the float switch. The SIGMA rainwater unit can also be switched manually to mains water operation at any time. A small top-up tank in the rainwater unit ensures an uninterrupted supply of water from the rainwater circuit.

Up to 97 % more energy efficient in standby mode than other rainwater units

The control systems of many makes of rainwater unit consume up to 15 watts in standby mode, by day and by night, 365 days of the year. This standby power consumption accounts for a large share of the energy required to operate a rainwater harvesting system. To solve this problem, WISY partnered up with the Mittelhessen University of Applied Sciences to develop the highly efficient ZETA 02 pump controller. This innovative device has reduced standby consumption to below 0.2 watts, a small revolution in its own way. Compared to conventional rainwater units, the ZETA 02 uses 97 % less energy in standby mode. The ZETA 02 is a standard component of the SIGMA rainwater unit.

Technical Data

Pump in wall unit Aspri Plus 15/3 Aspri Plus 15/4
Pump controller Zeta 02
Hydraulic data
Operating pressure 3,3 bar 4,4 bar
Max. delivery rate 65 l/min 65 l/min
Cut-in pressure of rainwater unit 1,5 bar
Min. cut-out pressure of rainwater unit 2,2 bar
Maximum starting frequency 20 times per hour
Pumped media filtered rainwater, drinking water (no sand content)
Volume top-up tank 9 l
Electrical data
Max. power consumption 608W 808W
Power consumption in standby mode < 0,2 W
Mains connection 230 V, 50 Hz, single phase
Rated current 2,7 A 3,5 A
Connecting cable SIGMA (pump controller) 1.4 m, with plug (3 x 1 mm²)
Float switch 15 m, cable head (3 x 1 mm²)
Water connections of wall unit
Inlet connection from cistern 1“ outside thread
Outlet connection to appliances 1“ outside thread
Mains water connection ³/₄“ outside thread
Noise emission
Rainwater operation 45 dB (A) 47 dB (A)
Mains water operation 63 dB (A) 63 dB (A)
Ambient conditions
Max. water temperature 35° C (95° F)
Max. ambient temperature 40° C (104° F)
Wall unit (width x depth x height) 500 mm x 315 mm x 510 mm

Item number

SIGMA 3 Without level indicator RZ 1003
SIGMA 4 Without level indicator RZ 1004