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Engineering LibreTexts

2: Components

  • Page ID
    11922
  • Built rainwater harvesting systems use various components to best meet needs. These components can be broken down into catchment surface, conveyance (gutters and downspouts), screens, first-flush, storage, water purification, and end-use (Figure 2-1).

    1. Catchment surface – area that the rainwater falls on to be captured.
    2. Conveyance (gutters and downspouts) – transports the water from catchment to storage or use.
    3. Screens – separates debris from the water.
    4. First-flush – diverts the first, and dirtiest, portion of rainwater.
    5. Storage – holds water for later use.
    6. Purification – cleans the water to the needed level.
    7. End-use – gives purpose to the system!

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    • 2.1: Catchment Surface
      The catchment surface is the area that the rainwater falls on to be captured. The catchment surface in a built (active) system is typically a roof. The catchment surface is important to some of the main questions, e.g., to determine how much water you can catch, how the water can be used, and what end uses are appropriate. The surface material and size is part of determining the total catchable volume.
    • 2.2: Conveyance (Gutters and Downspouts)
      Conveyance is what brings the water caught on the catchment area to where it will be stored and used. Gutters, downspouts, and piping serve to convey water from the catchment area to storage and end-use. Gutters and conveyance need to be sloped in the direction of water flow to prevent clogging, sagging, mosquitos, and damage from freezing.
    • 2.3: Screens
      Screens help keep a system clean. They do this by separating debris from the rainwater before storage, and often even before conveyance. Screens require maintenance, yet should serve to make that maintenance easier than if the debris was allowed to enter the rest of the system. Typical debris includes leaf litter and trash that has blown onto or been thrown on top of the roof.
    • 2.4: First-Flush
      The first-flush diverts the first and dirtiest portion of rainwater away from the storage and remaining system components. Pollution collects on the roof between rains and is subsequently washed during the beginning of the next rain. Typical pollutants include bird droppings and accumulated air pollution from car exhaust and industrial emissions. Long dry seasons, heavily polluted environment, and porous collection areas will raise the amount of pollution present on the roof before the rain.
    • 2.5: Storage
      Storage holds water for later use. Later use can be between frequent rains, requiring less storage volume, or in the dry season, requiring more storage volume. In all systems, it is important to think about weight, pest avoidance, and vacuum prevention. A vacuum can be introduced in a relatively sealed system by quickly evacuating the storage.
    • 2.6: Water Purification
      Water purification further cleans rainwater, depending on the end-use and need for purity. Rainwater harvesting water, especially in systems that use a first-flush, can be used for many applications without purification. For example, watering ornamentals needs no first-flush or purification, and watering edible plants depends on context. However, potable water always requires some purification.
    • 2.7: End Use
      An end use refers to how and where the water eventually will be used. There is no great reason to catch rainwater without an end use. Typical end uses include water for drinking, gardening, landscaping, cleaning, etc. As mentioned before, potable water is a greater challenge than other end uses, which may include cleaning, flushing, washing, watering, etc.
    • 2.8: Labels and Signs
      All systems need labels or signage that instruct and direct users. The most important label shows whether the system is potable or not. In addition to labels, consider nudges and point-positive design in your system. Nudges help users to do the right thing by gently reminding them. For example, if a user is intended to clean the borehole regularly, consider placing the first-flush nearby and facing a commonly used path so that the user sees the hole and is reminded.