Online monitoring of recycled water quality

Online monitoring of recycled water quality

Eva Reynaert, Deepthi Nagappa

Communities across the world face water supply challenges due to increasing demand,drought, groundwater depletion and contamination, and ageing infrastructure. In many regions, treated wastewater could be used as an alternative water source as it provides reliable quantities of water, all while relieving the stress on freshwater resources. The challenge for such systems is that safety, especially in terms of microbial water quality, must be ensured at all times.

In India, the reuse of treated wastewater has been getting increased attention due to rising pressures on water supplies, especially in water-scarce cities. In the city of Bengaluru, the Karnataka State Pollution Control Board (KSPCB) has mandated 100% wastewater treatment and on-site reuse (zero-liquid discharge or ZLD) for large apartment buildings since 2004. The treated water is reused for landscaping, car washing and more importantly, toilet flushing. However, there is limited information on short-term variations of the microbial water quality from such on-site water reuse systems, as water samples are usually sent to specialised (i.e., NABL-accredited) laboratories only once a month.  

This project evaluates the microbial water quality from on-site water reuse systems in Bengaluru and investigates strategies for real-time monitoring of the treated water. We will implement a range of commercially available and inexpensive online sensors in two existing water reuse systems and take daily samples of the microbial water quality. This data will then be used to train machine learning algorithms to predict microbial water quality using the sensor measurements. Ultimately, such monitoring algorithms could be used to send out an alarm when water quality targets are not met, and thus prevent residents from getting sick from using insufficiently treated water.

Installation of sensors at a decentralised water reuse system in Bengaluru

Automated measurement of bacteria concentration. These models, using sensor measurements to
predict the bacteria concentration, can replace complex and costly devices


Analysis of water quality parameters in ATREE’s laboratory

The knowledge generated in this research will be relevant for several audiences: 

  1. academics who are increasingly interested in field-based evidence of on-site water reuse systems,
  2. local regulators, who can glean information on how selected systems perform in the field and which parameters are crucial for performance assessment, and 
  3. building owners and operators of water reuse systems, for whom online monitoring can be linked to an increase in actual performance of the STP as well as an increase in trust by the residents/customers.

This project is a collaboration between ATREE, the Swiss water research institute Eawag ( and the university ETH Zurich (, with funding from ETH Zurich’s ETH4D program (