Rainwater Harvesting Systems for Container Houses: Intro

Rainwater Harvesting Systems

Rainwater Fundamentals

For many, harvesting rainwater is a matter of their eco-consciousness. Hopefully, it will be a growing trend because frankly, Mother Nature can’t make it anymore without our collaboration. However, for those that opted for living in an off-grid environment, harvesting rainwater is a matter of life. Certainly in the forefront of this trend is the community of enthusiasts of shipping container houses.

Before going further let’s see how the average US household uses this more and more precious resource – potable water. As can be seen from the pie-diagram below, more than half of the potable water is used for toilet flushing, outdoor activities (watering lawns and garden) and washing clothes. The next biggest water recipient is the bathroom and then finally, almost at the end comes the kitchen –the only place where the drinking-quality water is the must.
household-water-chart More than half of the water used by individual households can be easily replaced with rainwater. Source: Pure Water LCC (Arkansas, USA)

  • These statistics reflect a few important facts:

    a) Not every gallon of water is “equal”. Water used for toilet flushing, washing car and driveway or watering lawn does not have to meet the quality of drinking water;
  • b) Between the quality of Potable Water and Toiled Flushing Water, there is a large “grey” zone with different (and usually less restrictive) water quality requirements;
  • c) Low cost of municipal water systems and their convenience seems to be approaching the limits of sustainability. The deeply-rooted perception of abundance of freshwater is the reflection of the past. On our eyes, water becomes a precious and unfortunately more and more scarcely available natural resource;
  • d) Rising costs and frequent limitations of the use of municipal water due to droughts prompts to new, more sustainable solutions. And the best answer to these challenges seems to be the rainwater.

Note that gaining popularity dual-flushing systems noticeably decreased the amount of water used by toilets. Nevertheless, from the points of view of the water – toilets are still sort of black holes devouring enormous amounts of the highest quality potable water.

For obvious reasons, we will focus our discussion on Rainwater Harvesting System designed for typical household needs including utility water (toilets, showers, washing ….) and outdoor activities (garden, lawn, car-wash..). These account for the largest consumption of water and cause the biggest headaches in houses with limited access to water. The quality of drinking water must meet much stricter requirements (it’s regulated by the law) and so it will be discussed in a separate article.

Is it Legal to Harvest Rainwater?

Once we recognize the importance of rainwater, the next question is: Is it legal to harvest it? Once again, it is a matter of National/State/Local regulations. Critics point out that run-off water is crucial to sustain rivers and deep-water aquifers (not mentioning here potential claims of ownership). Such arguments, however, do not hold given the fact that:

  • a) Households use only 12% of supplied water (irrigation 36.6% and generation of thermoelectric power stunning 41.4%)
  • b) Most of rainwater harvested by individual homeowners will be anyhow returned to the ground (watering garden, lawn, washing car etc…).


US Daily water withdrawals. Source: United States Geological Survey (USGS)

Harvesting rainwater is legal over the territory of the US. Note, however, that individual states may put some restrictions (please check local regulations).

water-rights-usa

Legality of rainwater harvesting across the US. Dark Green (Encouraged), Light Green (Legal), Brown (legal with restrictions). Source: World Population Review

Note that some states offer financial incentives for rainwater harvesting (tax credits or exemptions), so please consult your local government.

And Good News: In some countries/states/provinces – restrictions applied to the use of water during prolonged droughts do not apply to stored rainwater. In other words – do you want to see you grass green? Harvest and store rainwater!

Rainwater Quality Requirements for Household Use

Unfortunately, there are no well-established, globally-recognized regulations governing the use of rainwater. In most countries, harvested rainwater in “as it is” form can be used for outdoor activities like watering lawns & “decorative” gardens. Also, the water for flushing toilets does not need any special treatment (provided that debris is filtered by sieves so you do not throw bulky stuff into the sewer). In general, however, higher quality water is required for indoor use. Putting aside potable water, the next level of water quality is required for:

    • a) Washing clothes
    •  b) Shower/bath

In both cases, the water should be clean, odorless and possibly free from pathogens, toxins and heavy metals (their acceptable level is regulated by law). The first two requirements should prevent discoloration of clothes, while the remaining three should guarantee harmless contact with skin and eyes. They are important because very often rinsing is completed with cold water that cannot “neutralize” pathogens. And when it comes to shower and bath, there is a strong possibility of swallowing water (especially by kids) not even mentioning exposure of skin (and wounds if any) to mentioned pathogens. The table below summarizes guidelines for the use of rainwater in individual households.


  • (1) Bathing quality water applies to swimming pools, but also rivers, lakes and sea (in generals areas where bathing and swimming are permitted). The water must meet some sanitary criteria for the level of biological (micro-organisms) and chemical (toxins) contamination. These criteria however are less strict and easier to meet than those for drinking water.
  • (2) Applies to ornamental gardens (water for veggies and fruits gardens may have some sanitary restrictions).
  • (3) Opposite to municipal water, rainwater does not contain dissolved minerals like calcium, magnesium, potassium (nor their chloride salts). It is much softer, healthier for our skin and hair. Thanks to low mineral content, rainwater is “easier” on washing machines, showerheads, water heaters, noticeably increasing their lifespan.

Rainwater Quality

Chemical Contamination

Theoretically, rain is the purest form of water in nature. Rain droplets are formed by condensation of water vapor, in other words, they are composed of “distilled water”. Practically, however, condensation requires micro-particles (dust) to trigger the process. Additionally, hovering in the air in the form of clouds, moving with the wind, droplets absorb gases and substances existing in the atmosphere. While the air pollution does not know borders, it’s probably safe to say that in remote rural areas the chemical contamination of rain will be very limited. In other words, most likely rain reaching the ground will meet the quality of drinking water.


Water cycle: Evaporation-Condensation-Precipitation-Open Surface Accumulation. Source: Ootsuk

However, next to big cities and industrial zones, pollution can drastically change this picture of “innocence”. Probably everybody already heard about “acid rains”! But this is just one example of what can happen to “distilled water” dropping from not that much “blue sky”.

Note also the impact of large-scale agriculture. It’s true that pesticides and fertilizers mostly contaminate the soil and with run-off waters – nearby rivers and deep aquifers. However, during their application (spraying by specialized aircraft but also by ground-level machines) they become airborne and can stay in the atmosphere for long!
Crop-Duster. Source: ScienceMag.org (American Association for the Advancement of Science)
Biological Contamination

Further contamination (this time possibly even more dangerous) takes place at water catching areas (typically roofs) and storing tanks. Excluding the potential impact of heavy metals (steel or copper oxides formed on metal roofs) as well as mentioned earlier dust, rainwater will face on its way down to the tank whole range of organic substances. Starting with birds’ droppings, dead insects, all sorts of pollen, leaves and thriving in this decomposing matter zillions of micro-organisms, bacteria and frankly, God only knows what. It’s a paradise for pathogens with consequences of serious, potentially life-threatening gastrointestinal illnesses.

However, as opposed to industrial contamination, the biological one can be controlled. Properly-designed rain harvesting systems with health-hazard free roofs, efficient first-flush diverts, sieves and storage tanks protected from insects and vermin can significantly reduce the impact of biological contamination. Such means can help to keep stored rainwater well within the limits of Bathing Quality.


Scary world of pathogens. Source: TestNeeds.com (Australia)

Bottom line – biological as well as heavy chemical contamination may severely limit the use of harvested rainwater to watering lawns and eventually flushing toilets. The task of filtering and disinfecting such rainwater may be economically unjustifiable for individual households.

That’s why before you move ahead with the project for rainwater harvesting, do thorough examination of the local environment. Note that for accurate and up-to-date pollution data you will need the help of local Environmental Agencies.

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