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Recharge Pit Design Guide: Dimensions, Filter Media, and Cost

Recharge pits are the workhorse of urban rainwater harvesting. This guide covers CGWB-recommended dimensions, filter media grading, cost estimates for typical Indian cities, and a construction supervision checklist to avoid the two most common failures — inadequate filtration and undersized inlet.

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CGWB dimension rules

Standard residential recharge pit: 1.5 m × 1.5 m × 3 m deep, with graded filter media in the bottom 2 m and a removable cover slab. One pit per 100–300 m² catchment depending on soil infiltration rate. The Expert engine adjusts this based on measured or modelled infiltration.

Filter media grading (bottom to top)

The graded filter is the single most important design element — it removes suspended solids while maintaining infiltration capacity.

  • 0.75 m — boulders 65–100 mm
  • 0.50 m — gravel 20–40 mm
  • 0.25 m — coarse sand 2–4 mm
  • 0.50 m — free space for water column
  • Cover — removable RCC slab with lockable inspection hatch

Cost estimate (2025 India rates)

Typical turnkey cost is ₹12,000–₹25,000 per pit including excavation, filter media, cover slab, and inlet connection. Cost is higher in rocky terrain (Bengaluru, Pune outskirts) and lower in alluvial soils (NCR, Kolkata).

Frequently asked questions

How often should I clean the pit?
Remove and wash the top 0.25 m of coarse sand annually before monsoon. Regrade the full filter media every 5–7 years. Rain GEO SAT reports include a printable maintenance calendar.
What if my soil has poor infiltration?
Rain GEO SAT will recommend a recharge shaft or borewell recharge structure instead. The Expert engine flags this automatically when infiltration rate falls below 15 mm/hr.

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Rain GEO SAT calculators use IMD, NASA POWER, Open-Meteo, and CGWB data to deliver engineer-grade rainwater harvesting and groundwater recharge designs.

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