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After the first part of our four-part Rainwater Harvesting webinar series, Rainwater Harvesting as a Runoff Reduction Tool, participants had the opportunity to ask our Rainwater Harvesting experts questions.

We didn't have enough time in the hour to answer all of the questions, so we are posting them here so that they are available to all.


These were the top 5 questions asked about Rainwater Harvesting Cisterns:

  1. Q: What are typical backfilling requirements? Open-graded aggregate around cisterns?
    A: Backfill requirements are dependent upon the structural requirements of the material used. Contech's Steel Reinforced Polyethylene and underground metal cisterns may allow in situ soil for part or the entire fill, depending on the quality of material. Other cisterns may only allow graded stone backfill. The backfill requirements are detailed in our submittal drawings, and can be found within our product pages.
  2. Q: Are the Steel Reinforced Polyethylene cisterns rated for potable use?
    A: The resin used for the SRPE cisterns has NSF 61 Certification for potable use, but we have not yet submitted the entire system for certification.
  3. Q: In regards to storage, is it recommended to circulate the stored water while it is waiting to be utilized?
    A: Circulation or aeration can be used if you anticipate a seasonal or sporadic demand. In general, if your demand is yearround, the water volume should turn over and additional equipment should not be necessary. Proper pre-treatment is also critical to maintaining a clean cistern. If organic material is left to decompose in the cistern, it can lead to fouling.
  4. Q: What filtration should be used for stormwater into a storage structure that cannot act as a settling basin (non-accessible for sediment removal)?
    A: It is vital to have access to your storage cistern. Even with a high level of pretreatment, fine sediment can still collect in the cistern and over the life of the cistern, there may need to be repairs made to the calming inlet, or to fix any watertight issues. Without access, the cistern would potentially have to be removed and replaced if any problems were found.
  5. Q: How do cast-in-place concrete installations compare to precast for large applications?
    A: Cast-in-place concrete installations can be great if a unique shape is required, or if the construction timeline is flexible due to the time required to build forms and wait for the concrete to cure properly. Precast concrete offers fast installation and pre-engineered structural designs. For a large area, this can mean freeing up land space faster and moving on to the building development.

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