Grey2Green

🌱 Inspiration

Singapore faces rising water demand, climate variability, and the looming expiry of the Johor water agreement in 2061. Meanwhile, centralized treatment methods such as NEWater and desalination are highly energy- and carbon-intensive[1].

Studies show that isolating and reusing greywater can save 30–38% of household water (mainly from toilet flushing and irrigation) while cutting operational costs and easing stress on freshwater sources[2].

This inspired us to propose Grey2Green—a decentralized greywater reuse system designed for housing estates and communities to help close the urban water loop.

💧 What it does

Grey2Green envisions a future where every community has a localized water loop:

Collect greywater from bathrooms, laundry, and sinks
Treat it locally using modular, low-energy systems
Repurpose treated greywater for non-potable uses such as:
1. Washing HDB corridors and outdoor areas
2. Irrigation of community gardens
3. Toilet flushing (which alone can account for ~30% of household water use[3])

By decentralizing treatment, Grey2Green reduces potable water demand, lowers energy loads from centralized treatment, and increases climate resilience.

🛠 How it could be built

Modular treatment units designed to fit within HDB/community infrastructure
Separate piping collection for greywater sources
Scalable treatment process (sedimentation, filtration, low-energy disinfection)
Designed for compliance with PUB non-potable water reuse standards[4]

⚡ Challenges to anticipate

Accurate dimensioning and integration with existing HDB layouts
Regulatory compliance with PUB safety and health standards
Community acceptance and trust in using treated greywater for shared spaces

🏆 Potential impact

Reduce potable water demand in housing estates by up to 30%[2]
Lower carbon footprint compared to centralized wastewater treatment[5]
Support Singapore’s transition toward a circular and resilient water economy
Provide opportunities for community engagement in sustainability practices

📚 What we expect to learn

How community-scale systems compare economically with centralized systems
The role of scale and density in determining efficiency and payback periods[6]
Insights into user acceptance and behavioral change in shared water systems

🚀 What’s next for Grey2Green

Develop design prototypes and conduct feasibility studies for integration in new HDB developments
Collaborate with PUB and policymakers to establish frameworks for decentralized water reuse
Explore expansion opportunities, including rainwater harvesting and IoT-based monitoring
Pilot Grey2Green in selected estates to generate data for scaling into future green towns

📑 References

[1]: Li et al., Greywater reuse potential in urban sustainability, Journal of Environmental Management (2020).
[2]: ResearchGate, Approximate generation percentage of wastewater and greywater (2014).
[3]: PUB Singapore, Water Efficiency Measures in Buildings (2024).
[4]: PUB Singapore, Technical Guidelines for Water Reuse (accessed 2025).
[5]: Lemos et al., Life cycle assessment of decentralized water reuse, Science of the Total Environment (2021).
[6]: ResearchGate, Energy consumption for greywater treatment system in Japan (2015).