Rainwater Harvesting Tank Sizing

Ref: MSMA 2nd Edition (2012), Chapter 6 — Rainwater Harvesting; Eq. 6.1, Tables 6.2–6.4

MSMA Equation 6.1 sizes the RWH tank as St = 0.01 × Ar (m³ per m² of roof) — equivalent to 10 mm of rainfall storage per unit roof area. This is a near-optimum value with ± 25 % variation (§6.4.5). Annual yield (AARY) values are scaled from Table 6.4 (base case: 1 m³ tank + 100 m² roof). For more accurate sizing, use the daily water balance model described in §6.4.3.

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St = 0.01 × Ar (tank size m³ per roof area m²)

Ref: MSMA 2nd Edition (2012), Chapter 6 — Rainwater Harvesting; Eq. 6.1, Tables 6.2–6.4

Roof Catchment Area (Ar) (m²)

Plan (horizontal projected) area of the roof

Nearest Town (Table 6.2 / 6.4)

Daily Rainwater Demand (optional) (L/day)

e.g. toilet flushing 120 L/day, car wash 200 L/wash — see MSMA Table 6.1

Recommended Tank Size (St)

—m³

Engineering aid only — final design must be endorsed by a registered PE under BEM.

Disclaimer: This output is an engineering calculation aid only and does not constitute a final or endorsed design. All designs submitted to Malaysian authorities must be endorsed by a registered Professional Engineer (PE) under the Board of Engineers Malaysia (BEM) in accordance with the Registration of Engineers Act 1967.