How can we estimate greywater and blackwater generation at household level?
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I want to know how can we clearly distinguish between two, we the exact proportion or by any thumb rule.
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Wastewater generation at the household level can be estimated by calculating the total wastewater output, which is generally about 80% of the total daily water consumption, as per CPHEEO manual (CPHEEO, 2013).
For instance, in a standard Indian household of five persons using 135 litres per capita per day (lpcd), the total wastewater generated is:
• 5 × 135 × 0.8 = 540 litres per day.
This total wastewater is split into:
• Greywater (from bathing, washing, and kitchen use): usually 65–80% of total wastewater.
• Blackwater (from toilet use): makes up the remaining 20–35%.
Assuming a 75:25 greywater to blackwater ratio, the same household would generate approximately:
• 405 litres/day of greywater, and
• 135 litres/day of blackwater.
Additionally, per capita estimates for different conditions suggest:
• Greywater: 70–100 L/person/day
• Blackwater: 20–40 L/person/day
• (Source: IRC, 2020)
These values can vary depending on user behaviour, toilet technology (pour-flush, dry toilets, etc.), and water availability.
