With more than 30 years’ experience in the residential and commercial water treatment space, Mark Nelson is a Class 1 Drinking-Water Operator and a CBWA (Canadian Bottled Water Association) Certified Plant Operator. As founder and president of Nelson Water in Ottawa, Mark focuses on dealing with challenging water treatment system designs for problem water. He also heads the largest water bottling plant in the city of Ottawa with a delivery network throughout the Valley.

In certain regions of the world, people are reliant on rainwater to supplement their meager water reserves. In fact, even in the developed world, this practice has been adopted by homeowners, farmers, and even industrial production facilities. Rainwater can be useful, but there are safety considerations and it can be hard to decide if it’s a good fit for your home or business. In this article, we will present a brief primer on rainwater harvesting to help you make an informed decision.

Understanding Rainwater Harvesting

Rainwater harvesting is when rainfall is collected and stored to be used for drinking, bathing, cleaning, irrigation and many other applications. The rain is usually collected in the form of run-off from a structure (typically a roof) via gutters and a directed downspout. The harvested rainwater is then directed to a storage tank or it may be used to replenish the groundwater supplies under your property. A rainwater harvesting system can be a simple downspout leading to a barrel or something far more complex. Larger harvesting systems can fill large cooling towers in an industrial facility and with proper treatment this water can be used for drinking and cooking. Let’s take a closer look at three common rainwater harvesting systems in more depth, they are: rain barrels, a dry system and a wet system.

A Rainwater Barrel

This is an economical way to get started with rainwater harvesting with a simple plastic barrel. A rain barrel is easy to find at your local home improvement store and they are inexpensive. Simply place the rain barrel under a downspout to collect the rain that is diverted from the roof. A rain barrel typically holds around 180L of water and the better models have a spigot located near the base. This allows you to draw water from the barrel or you can attach a garden hose or irrigation system. This is a cost effective way to water your plants when there is less rainfall but drinking is not advisable.

A Dry System

These rainwater harvesting systems can typically store larger volumes of water when compared to a humble rain barrel. But, the basic idea is the same, the water that falls on a structure is diverted to a large water storage tank. They are called dry systems because the pipes will dry in-between each period of rainfall to fully fill the tank due to gravity.

A Wet System

This is a very different system than the rain barrel and dry system approach to rainwater harvesting. The pipes are buried underground, when the rain falls, it flows into these pipes from the gutters. Then the water gradually rises via a vertical pipe to fill an external storage tank that may be buried underground. As the name suggests, these pipes are wet at all times and they never dry out between periods of rainfall. For this reason, wet harvesting systems are pretty vulnerable to stagnation, which in turn can lead to anaerobic fermentation and mosquito infestations. To prevent these issues, it’s important to install screens on the pipes and to drain them regularly. Although this may seem like more work, many people prefer wet systems because the pipes are hidden and they can be located further away from the property.

Does a Rainwater Harvesting System Require a Pump?

If you intend to use the rainwater in your home or at some location far away from the storage tank, the answer is probably yes. A demand pump will extend the usefulness of your harvesting system and allow you to use the water in more ways. A reliable option is a water booster pump that moves water based on the volume of flow you need. This allows you to move the rainwater to any tap located inside or outside of your home with sufficient water pressure. Another option, if you have a water storage tank located above the height of your home, is a gravity fed system. This forces water down and out of the tank, but its uses are limited and the water pressure is typically lower.

Is it Safe to Drink Rainwater?

And by extension use, if for cooking and other tasks? The answer is a tentative yes, but this must be qualified because contaminants may be present. In theory, the rainwater is naturally clean because it’s distilled in the atmosphere before it falls as rain. But, as soon as that rain falls it can accumulate airborne and surface contaminants. The airborne contaminants can include atmospheric pollution, dust, dirt, and more. This type of contamination is more prevalent in urban locations where more activity takes place. The surface contaminants can include bacteria, pesticides, bird poop, dust, dirt, and more. These materials are washed into the rain as it’s collected from the roof and into your chosen storage tank. For these reasons, it’s not advisable to drink rainwater unless further filtration has taken place to remove any contaminants that may be present.

How Do I Clean Rainwater?

Although it is possible to clean the water by distilling it, this is a poor choice for a few reasons. Distillation is the collection of steam generated when the water is brought to the boil and maintained as a “rolling boil”. This is usually achieved in a water distillation unit, but boiling water for long periods of time consumes a lot of energy. When the water has been distilled, it must be left to cool before it can be decanted into sanitized storage vessels. This is time consuming because it can take quite a while for the water to cool and storing that water can take up a lot of room.

What is the Alternative?

The best way to clean your harvested rainwater is to pass it through a reverse osmosis (RO) filtration system. Boiling water can remove bacteria, but a RO system can remove many more types of contaminants, including Volatile Organic Compounds (VOCs), pesticides, herbicides, dissolved solids, heavy metals, and more. If you have concerns about microorganisms, you can add an ultraviolet (UV) light to disinfect the incoming rainwater. It is possible to add multiple filtration systems to deal with specific quality issues or to add some extra “polish” to the water.

If you want a RO filtration or a UV purification system for rainwater harvesting, contact your local water treatment specialist today.