This technical note discusses the Rainwater Harvesting with HDPE Pipe Cisterns September 2024. Introduction, layout, capacity, installation, liner and design explained.

For the past several years, the use of smooth interior corrugated high density polyethylene (HDPE) pipe has been a viable alternative for the control of stormwater quality through underground systems. Typically, stormwater has either been infiltrated through perforated pipe or detained in solid pipe and then discharged at a controlled rate to the local storm sewer system or tributary. In both situations, the design did not provide for the potential reuse of stormwater. There is a growing demand for the construction industry to provide for resource reuse. In some situations, the reuse is being driven by a regulatory requirement. In many cases, the reuse of resources can provide an economic benefit. This is especially applicable to stormwater in areas where water resources are at a premium. Water reclamation should be considered in situations where infiltration is not feasible due to site constraints.

A typical cistern layout includes at least one inlet into the system. This inlet can be on the cistern manifold as shown below or can be done on a lateral. Further, the inlet can be accomplished via a pre-fabricated stub or with a reducer and tee fittings in the system corner. The outlet of the cistern should be directed to a reinforced concrete manhole. Figures of layout are provided.

Storage capacity is shown through a table with the values for inside/outside diameter, spacing, volume and total storage.

For a cistern installation, ADS N-12 perforated pipe embedded in a Class I crushed stone backfill is recommended. A typical cistern cross section figure is provided.

The thermoplastic liner, puncture resistance needs to be considered. This can be addressed by the placement of non-woven geotextile on either side of the membrane. The liner seam, if applicable, should be watertight to maintain the integrity of the system. Pipe “boots” need to be pre or field fabricated for locations where system piping is either entering or exiting the cistern footprint, i.e. inlet and outlet piping. A detail depicting the liner “boot” is shown.

A cistern design bed size calculation is provided with technical assistance guidelines.