How to Calculate Gray Water
What is Gray Water?
Gray water reuse captures wastewater from sinks, showers, laundry for non-potable uses (irrigation, toilet flushing). Reduces freshwater demand.
Step-by-Step Guide
- 1Typical household: 50-80% of wastewater is gray water
- 2Treatment options: simple settling, biofilter, or UV disinfection
- 3Using gray water reduces freshwater demand 30-50%
Worked Examples
Input
Household 200 L gray water daily, uses 100 L for toilet/irrigation
Result
Freshwater reduction: 36,500 L/year
Equivalent to 1-2 months supply
Common Mistakes to Avoid
- ✕Mixing gray water with black water (toilet)
- ✕Over-storing gray water without treatment (odor and contamination)
Frequently Asked Questions
What's safe to include in gray water?
Sink, shower, laundry water. Exclude toilet (black water), which requires separate treatment.
How long can gray water be stored?
Without treatment: 24-48 hours (anaerobic bacteria grow). With UV/chemical: up to 1 week.
Ready to calculate? Try the free Gray Water Calculator
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