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A Rainwater Harvest System Design for Your In-House Plumbing Needs

I write because I'm curious and love learning something new. This is a subject that sparked my curiosity and I wanted to know more about.


There are many water sources for in-housing plumbing. Well water, spring water, surface water, and municipal water are all choices for non-potable and potable uses. These forms of water sources are all surface-type sources.

Surface-type water sources can be contaminated with surface-type contaminants such as fertilizers, decaying vegetation, and even man-made runoff contaminants such as oil from cars and city storm runoffs. Surface-type water sources can be contaminated with fluoride, calcium, magnesium, iron, hydrogen sulfide gas, and other naturally occurring contaminants.

So what makes rainwater different from these surface-type water sources?

Why Rain Harvesting?


Rainwater is the purest form of water that is naturally found. When the rain falls from the roof, organic material, such as carbon dioxide, pollen, and other organic matter can come in contact with rainwater but never inorganic matter or any contaminants found on the surface of the earth that could contaminate other sources of water.

A rainwater harvest system design can be beneficial for many things like gardening and landscaping, farming, washing the car, and even hooking up a rain harvesting system for a plumbing source for non-potable and potable uses.

Imagine having a constant, filtered water source to drink, used to take a shower, or flush toilets with and not have to pay for municipal, chemically treated water.

Is this even possible? With an efficiently designed rain harvesting system, the answer is yes. Let's take a look at the different parts of a rain harvesting system and how they work together.

Gathering Rain


Gathering the rain is not as simple as putting barrels outside and catching the rain as it falls. This might work somewhat if you don't need a lot of rainwater, let's say, to use just to wash a car or water a garden.

But, if you plan to use the rainwater as your sole source for in-house plumbing, you're going to have to make sure that you can collect as much as possible while it rains. That means positioning or connecting the water caches to a concentrated source of rainwater, like the roof.

Since the rainwater may be for drinking and cooking as well, the fewer contaminants that the water touches while being collected, the higher quality the water will be for those uses. The type of roofing that the rainwater cascades over can make a difference in quality.

Roof Types Best for Collected Rainwater


Two things to consider when connecting a rainwater harvesting system to a roof. What will you be using the water for and how much water loss will you be able to stand?

Some roofing materials are capable of providing higher quality, cleaner water than others and can be more efficient in providing more water at one time than other roofing materials.

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Some roofing materials are treated with chemicals that can degrade the quality of water and some materials can slow and lessen the stream of rainwater being collected. But depending on what you need the rainwater for, these considerations may not be a factor

For example, tin is the best roofing material for harvesting rainwater, especially for potable uses, because tin does not leach chemicals into the rainwater as long as it has the proper coating. Likewise, there is very little water loss with a tin roof, maximizing the collection efforts.

Here are some examples of roofing materials best used for potable and non-potable uses.

  • Tin
  • Clay
  • Ceramic
  • Cement
  • Rubber

Asphalt shingles can work with rainwater collection, but there can be certain contaminants leached into the water making the rainwater not even suitable for irrigation purposes.

Wood, cedar, and shake shingles can leach contaminants and retain mold and algae making the water suitable for irrigation but not for drinking or cooking.

What Kind of Conveyance System is Needed in Rain Harvesting?


The next step is to figure out how the rainwater will be diverted into a storage system.

There are two types of conveyance systems.

  • A gravity-fed conveyance system consisting of a downspout and underground pipes feeding the storage containers below grade.
  • A wet-conveyance system requires downspouts to be replaced with a sealed conveyance. The water that fills up in the sealed conveyance will be gravity-driven into storage containers that are level or above grade.

Pre-storage Filters


These are helpful in not only filtering out large contaminants from the roof, such as leaves and twigs but also oxygenates the water keeping it fresh and pure.

The Storage Tanks and More Filtering


A little-known fact about the metal or polyethylene tanks that store the rainwater is that there is a healthy microbiological layer, called a biofilm, that forms on the bottom of the tanks. This film keeps the water clean.

In order not to disrupt this film, the water is not forced to the bottom of the tanks but goes through a smoothing inlet which sends the water into the tank in an upward motion.

A pump mounted onto the inside of the tank sends the water through a series of filters that removes even more contaminants and makes the water taste wonderfully fresh.

A sediment filter removes any remaining particles. Next, the water flows through a carbon filter still removing even more contaminants and contributing to the taste of the water. The last filtration step is an Ultraviolet (UV) disinfection system. Any possible bacteria is removed using this filtering technique.


Now, you might be saying to yourself, "What happens if not enough rain is collected to sustain my in-house plumbing needs? What if I run out of water?".

This is not a problem. If the water runs out due to drought or for any reason at all, there is usually an automatic crossover to a secondary supply, whether it be municipal or well water.

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