Rainwater Harvesting & Recharge
Putting rainfall back into the ground instead of down the drain.
Overview
Collecting rain off roofs and paved areas, carrying it to a recharge structure and letting it soak back into the ground, as state building rules now require. The job is the opposite of stormwater drainage: the water is held and soaked away rather than carried off.
Specification
- Product range: Alcorr DWC HDPE (Perforated + Solid)
- Standard: IS 16098 (Part 2)
- Conveyance Sizes: ID 100 mm to ID 600 mm
- Recharge Sizes: ID 150 mm to ID 1000 mm
- Standard Code: IS 16098 (Part 2)
Why HDPE here
- Perforated lengths soak water away along the whole run, not just at a pit
- Nothing leaches out of the pipe into the water it puts back underground
- Light enough to install inside a finished plot without heavy machinery
Typical deployments
- Rooftop down-pipes
- Recharge trench and pit liners
- Percolation galleries under paving
- Storage tank inlet and overflow
Specification and site notes
First flush before anything else
The first few minutes of a storm wash off everything the roof has collected: dust, bird droppings and leaf litter. A first-flush diverter that discards that volume is what keeps the recharge structure from silting up, and it is the part most often cut from the budget and most often the reason a system stops working.
Percolation rate sets the geometry
The recharge structure is sized by the soil's infiltration rate against the design storm, not by roof area alone. Run a percolation test on the plot first. In low-permeability soil a trench with a long perforated run outperforms a deep pit, because infiltration happens over the whole wall area. On campus and township schemes that run can be ID 600 mm to ID 1000 mm DWC, which stores the storm volume as well as infiltrating it, and at those diameters a length weighs about an eighth of the RCC equivalent.
Perforated in the gallery, solid on the way there
The run from the down-pipe to the structure is solid-wall, so nothing is lost or picked up on the way. Only the run inside the recharge trench or gallery is perforated. Wrap that section in geotextile within a graded aggregate surround, or the slots clog with fine soil in a season or two.
Keep it serviceable
Bring a silt trap and an inspection chamber to the surface ahead of the recharge structure and record where they are. A recharge system nobody can desilt is a system that quietly stops recharging, usually without anyone noticing until the borewell yield falls.
FAQ
How is rainwater harvesting piping different from stormwater drainage?
The duty is reversed. A storm drain carries water off the site as fast as it can; a recharge system holds it and infiltrates it into the ground. That changes the design: perforated pipe in a granular surround inside the structure, a silt trap and first-flush diverter ahead of it, and geometry set by the soil's percolation rate rather than by peak discharge.
What sizes are used for a recharge system?
ID 100 mm to ID 200 mm for roof down-pipes and the run across a plot; ID 150 mm to ID 1000 mm perforated for recharge trenches and percolation galleries on campus and township schemes, where the largest bores store the storm volume as well as infiltrating it.
Does the whole run need to be perforated?
No. The run from the down-pipe to the structure is solid-wall, so nothing is lost or picked up on the way. Only the run inside the recharge trench or gallery is perforated, and it should be wrapped in geotextile within a graded aggregate surround.
Why do recharge structures stop working?
Silt. Either the first-flush diverter was omitted and the roof's accumulated debris went straight in, or the perforations clogged because there was no geotextile envelope, or the silt trap was never desilted. All three are avoidable at design stage and expensive to fix afterwards.
Commonly specified sizes
At ID 1000 mm a DWC length weighs about an eighth of the same size in RCC and goes in without a crane, so the biggest sizes are where it beats concrete by the widest margin.
Related applications
See also
For CAD drawings, compliance certificates and B2B pricing estimates, contact mktg@alom.in.
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