Rainwater Harvesting Tanks – Everything You Need to Know

The storage of harvested rainwater in tanks is a fairly simple method. The complexities may arise while deciding over the size and material of the tank. This blog covers literally all the aspects related to rainwater harvesting tanks- what material is best suited, what size to choose and more.

The practice of rainwater harvesting is gaining its sustainability with more and more people contributing to the cause, along with the government intervention at the Central, State and local level. The information resources available online are proving helpful too. Probably, the most asked question is about how the water can be stored safely after it has been collected from rooftops or other catchment areas (concrete patios, driveways, and other impervious surfaces). More questions follow thereafter.

Water tanks are used to store collected rainwater, transferred via pipes. It is important to understand the characteristics of the suitable type of water tank for your rainwater harvesting system.

Identifying Size of the Tank

To know what size of the tank you might need, consider the following factors:

  • Rainfall – the average annual rainfall, the pattern of distribution throughout the year and the variation from year to year.

A tank of capacity less than 5000 litres will provide a good proportion of water use for the areas with year-round rain; for areas with dry summers, a much larger tank of around 10,000 litres is a required.

  • Area of the Catchment

Catchment Area (often roofs, in square feet, ft2) x Event Rainfall Depth (in) x 0.623 Conversion Factor = Gallons of Potential Rainwater Collected

  • Security of Supply Required – to lower the risk of a tank running dry, especially if the intended tank is the sole source of water supply, chosen size must provide a higher level of security. A tank, less than 30,000 litres might work in such a scenario.
  • Demand – the number of family members, their water use habits, the intended use of water and season.
  • Purpose a rain barrel of about 240 litres or rainwater tank of 500 litres+ is enough for garden watering.

A larger tank is needed if rainwater is to be used for indoor supply.



Choosing Material for Your Rainwater Harvesting Materials

The most prevalent rainwater catchment tanks around the world are composed of virgin polyethylene. Other available materials are plastic (polyethylene), concrete, galvanized steel, as well as fiberglass and stainless steel which are rust and chemical-resistant.

Each of these materials has its own pros and cons. The selection of the type majorly depends upon the external environmental conditions. For instance,

  • polyethylene tanks are subject to algae growth and short life due to UV exposure in the sunlight.
  • A specific coating is needed for fibreglass and galvanised tanks to have them in potable grade. The coating also prevents rusting at any welded seams.
  • Concrete tanks have issues with leaching of lime into the stored water.

There is one more aspect to consider – the contamination within the tank due to materials used in the surrounding components of the RWH systems.

Contamination Alerts

Apart from the air and industrial pollutants that can contaminate the stored water in the rainwater harvesting tanks, the following can cause serious contamination:

  • Lead-based, Zinc-based paints and Tar based coatings used on the roof may cause contamination and bad water taste.
  • Galvanized iron or ZINCALUME (Zinc-Aluminium alloy) roofs are not recommended if transported water is intended for portable use.
  • Acrylic paints on the roofs may become the source of detergents and other chemicals which gets dissolved in the runoff.
  • For the entire winter season, the runoff from fibrous cement roofs must be discouraged as it promotes leaching of lime.
  • The roof catchments must not use chemically treated timbers and lead flashing.
  • The rainwater collected from the parts of the roof which incorporate flues from wood burners must not be used without a high degree of filtration.
  • The rainwater tank must not have discharged feed from roof-mounted appliances such as air-conditioners or hot-water systems.
  • The water with high acidity, stored in plastic tanks and then made to travel through copper pipes can cause water poisoning due to instability in the pH balance. Though, plastic tank is an inert container.
  • Metallic roofs can react with steel tanks and can cause corrosion, making stored water unfit for drinking and cooking.

Improperly sealed rainwater tanks are the best site for breeding grounds of mosquitoes. Underground tanks are most preferable to avoid mosquito’s contamination as they are dark and keep the water too cool (12.8oC) which is just perfect for killing any mosquito larvae, bacterial and algae growth.

Desludging must be practised at least every 2-3 years and wash or flush new tanks before use.


Estimated Cost of RWH tanks

The installation of a rainwater tank is really easy and inexpensive. For a rough idea, the cost of the RWH plastic tank lies somewhere from Rs 2/litre to about Rs 3.5/litre. In total, the cost depends upon the material, installation and delivery requirements. Additionally, the cost of pipes, filters or treatment, plumbing requirements (if any), consent fees and yearly inspection fees can sum up the cost of a well-equipped storage tank.

The required quantity of water for landscaping or gardening in homes can be sufficiently contented by rain barrels. For more affordable solutions, inexpensive household products such as food storage, transport barrels, etc. can be used to craft the rain barrel.

The proper choice and maintenance of the rainwater harvesting storage tank will ensure a safe water supply. Every rainwater harvesting system has its own requirement for storage. Evaluate each consideration, put them together and chose the most suited option. Also, check with your state and local authorities regarding the need for the consent if, a very large or elevated tank is to be installed.


Chaitanya’s well-experienced team is here to serve you

Our well-knitted team of engineers and technicians have all the experience to present you with best-suited solutions, for almost any query of yours. The rainwater harvesting feasibility reports are generated to understand whether it is sustainable to have an RWH system installed at the chosen site.

Our innovative rooftop filters help to prevent the contamination of water, stored in the storage tank. from the debris and other solid contaminated substances.

For rainwater harvesting systems at larger scale and area, we make gravels and RCC fume pipes collar rings available at reasonable cost.

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