To determine the rainwater tank and gallon size that best suits your unique scenario: understand five (5) rainwater harvesting (RWH) variables. These key details are selective to RWH systems and should be considered prior to implementing a system and the rain tank that meets the size for your individual application and needs.
Key Detail Variables of a Rainwater Collection System
- Annual, local precipitation rates;
- Size of the catchment area, which are often roofs;
- Gallons of rainwater potentially captured during rain events;
- Application water usage and volume requirements, and;
- The balance between rainfall supply and water usage demand.
A correctly sized rain barrel should be rated to a max gallon capacity suitable to:
- Supply regular water use needs;
- Collect sufficient rainwater volumes for applications;
- Store and maintain rainwater for use between average rain events.
Considering the Details
The details and components of a RWH system influence rainwater capture potential, and this directly links to selecting the rain barrel volume capacity that will be most appropriate for your select harvest scenario. The five RWH variables are outlined and expanded below:
(1) Precipitation Amounts, Rain Tank Filling
- Regional rainfall is extremely dependent on location; you can only use as much rainwater as falls from the sky. Understanding your rainfall potential is very important in successful RWH systems.
- Implementing a large rain barrel may not be best if it may never be fully filled when considering local precipitation rates and your water usage amounts.
- Research indicates rain barrels that regularly fill and make use of the tank overflow can maintain better water quality due to off-flow of stale water or washing of potential floating contaminants that may make it through the upstream pre-filter. The applicability of this concern may be based on the individual scenario.
(2) Rainfall Catchment Area, Roofs
- The total size of the area designated for rainfall impact and collection directly correlates with the total volume of water that can be harvested during a rain event.
- The majority of rainwater harvesters use their house roofing as rainfall catchment areas, incorporating gutters and downspouts into RWH systems.
- Roofs make very effective tools for rain capture but can experience some water quality concerns with certain roof materials. Metal roofs have the greatest cleanliness capabilities and are most recommended for rain harvesting; common asphalt shingle roofs have particulate and potential chemical concerns where RWH accessories may be necessary to achieve the desired water quality.
- All catchment areas are recommended for first-flush diverters to discharge the first rainfall that may contain built-up roof contaminants. Think of this like pre-washing the roof for potentially collecting clean water run-off.
- Catchment areas, by definition, can be any structure designed to take rainfall and channel it to a system of plumbing components and the storage tank for rainwater capture and use.
(3) Gallon Capture Potential
- A rain harvesting system’s gallon capture potential depends on the inches of regular rainfall and the size of the catchment area:
- More rain = increased capture potential
- More catchment area = more collected rainwater
- More collected rainwater implies a potential to install a larger tank with an increased gallon size capacity. An increase in rain barrel capacity could allow one to use rainwater for more applications as well as better manage supply and demand.
(4) Application(s) Water Requirements
- Know and/or plan your rainwater use application with an understanding of your actual or anticipated water use volume in order to select a rain tank capacity that is sufficient to provide the water you need.
- Depending on entire water quality and level of applied treatment, rainwater may only be appropriate for certain applications. Implement a system designed to provide the rainwater quality rainwater you need for your desired uses.
(5) Balancing Supply & Demand
- Balancing supply and demand is the most intricate detail of optimizing a RWH system and selecting the right size rainwater collection tank, especially if seeking to rely on your rainwater supply alone.
- To better understand your water balance compare: (a) your regular, expected rainwater capture volumes with, (b) your regular water requirements from uses.
- When considering rainwater balance, it is important to compare using similar time-frames. Consider analyzing both monthly and yearly (or seasonal) time-frames for an overall picture of both your incoming rain supply and outgoing water usages.
National Tank Outlet | America’s Liquid Tank Superstore
At the end of this article, it is our hope here at the National Tank Outlet that you have a better understanding of the key variables that drive an effective rainwater harvesting system and how they all interlink together for selecting the rain collection tank that is the right size for the job.