How Do Rainwater Tanks Work?

With water scarcity, environmental sustainability, and rising costs of utilities, rainwater tanks are becoming a valuable asset for homeowners and businesses.

By collecting and storing rainwater for later use, these tanks are an eco friendly and cost effective way to manage water.

Whether for irrigation, household use or drinking, rainwater tanks can reduce your reliance on mains water.

But how do these tanks work and what do you need to know about using one? This article will break it down from rainfall collection to water use.

Rainwater Collection 101

Rainwater tanks work on a simple principle: collecting rain that falls on your roof and storing it for later use. The roof is the most critical part of a rainwater harvesting system as it is the primary catchment area. When rain hits the roof, it flows down into the gutters and downpipes and into the storage tank.

The type of roof can affect the quality and quantity of water collected. For example, smooth surfaces like metal sheets collect more water, while rougher surfaces like tiled roofs can trap some water.

Also note that roofs made of certain materials such as those with lead-based paints can contaminate rainwater and make it undrinkable without proper filtration.

Gutters and downpipes also play a big role in the collection process, guiding the rainwater into the tank. Without an efficient gutter and pipe system, water can overflow and reduce the efficiency of your rainwater harvesting setup.

Make sure these components are clear of debris like leaves and twigs to maximize water collection.

First Flush System: Removing Impurities

Once rainwater flows through your gutters, the first step before it enters the tank is the first flush system. This critical component diverts the first few millimeters of rainfall which contains the highest concentration of contaminants like dust, bird droppings, and other organic matter away from the tank.

Why is this necessary? The first rain after a dry period washes down the debris accumulated on the roof.

By diverting this initial "dirty" water away, the first flush system ensures that the water stored in your tank is of better quality. Only after this initial wash-off is completed does the cleaner rainwater enter the storage tank.

Many first flush systems are automatic and require minimal maintenance but it’s good to check them periodically to make sure they are working properly.

Regular checks will help you identify any blockages or damage and prevent poor-quality water from entering your tank.

Storage: Rainwater Tanks

The water that passes through the first flush system then enters the storage tank. Rainwater tanks come in different sizes, shapes, and materials to suit different needs.

Common materials are plastic (polyethylene), concrete, metal, and fiberglass. Each has its pros and cons; for example, plastic tanks are lightweight and easy to install while concrete tanks are very durable and can be installed underground for space saving.

The size of your rainwater tank will depend on several factors such as the size of your roof catchment area, your local climate, and your water usage needs.

In areas with frequent rainfall, smaller tanks may be enough but in drier regions, larger tanks are usually required to store enough water for dry periods.

Also, the intended use of the water will determine the tank size. If you plan to use rainwater for household uses like laundry and toilet flushing you will need a larger tank than if you will only use it for garden irrigation.

Positioning of the tank is also important. Most rainwater tanks are installed above ground but in some cases, tanks are installed underground to save space or for aesthetic reasons.

Underground tanks are more expensive to install but offer the benefit of being out of sight and less prone to temperature variations which helps keep the water cooler and reduces evaporation.

Filtration and Treatment: Making the Water Safe for Use

While rainwater is cleaner than many other natural water sources, it still needs to be filtered before it can be used for certain purposes especially if it’s for drinking or household use.

Most rainwater tank systems have multiple layers of filtration to ensure water quality.

Basic filters, usually placed at the inlet of the tank, catch large particles like leaves and twigs.

Finer filters inside the tank will catch smaller debris like dirt or pollen. Depending on your intended use of the water further treatment may be required.

If the water is for drinking or cooking additional filtration and disinfection methods like ultraviolet (UV) sterilization or chlorine dosing should be considered to kill any bacteria or viruses that may have entered the system.

But if the water is only for irrigation or outdoor cleaning then extensive treatment may not be required. For non-potable uses like toilet flushing or laundry a basic filtration system is usually enough.

Pumps and Distribution

In some cases the stored rainwater can be used directly through a gravity fed system especially if the tank is higher than the point of use. But many rainwater tank systems require a pump to deliver the water with enough pressure.

This is especially true if the water is used for household purposes like flushing toilets, washing clothes, or showering.

Pump systems are usually automatic and will activate when a tap connected to the rainwater system is turned on.

Some pumps also have pressure tanks which store a small amount of water at high pressure so the pump doesn’t need to activate every time water is drawn.

This reduces wear and tear on the pump and ensures a more consistent water supply.

Overflow Management: Managing Excess Rainwater

During heavy rainfall, tanks can fill up fast and to prevent flooding or damage they are equipped with overflow systems.

These mechanisms will divert any excess water away from the tank and into a designated drainage area or back into the stormwater system.

Without an overflow system, rainwater will spill over the top of the tank potentially damage the surrounding area and reduce the efficiency of the water collection process.

For safety overflow should be directed away from the building’s foundation to prevent structural damage or erosion.

Using the Water: Many Uses

The water in a rainwater tank can be used for many purposes depending on the treatment and filtration.

For outdoor uses like garden irrigation, washing cars, or cleaning patios untreated rainwater is usually enough. But for household uses like flushing toilets, washing clothes, or drinking the water must meet certain standards.

In some areas, regulations dictate how rainwater can be used especially for potable purposes.

You need to know these local rules and make sure your filtration and treatment systems meet the safety standards if the water is for drinking or cooking.

Maintenance: Looking After Your System

While rainwater tanks are low maintenance, regular maintenance is required to keep the system running smoothly.

Gutters and downpipes should be cleaned regularly to prevent blockages and the tank should be checked for any signs of contamination or damage.

And the filters will need to be cleaned or replaced from time to time to keep the water quality high.

In some cases, a layer of sludge can accumulate at the bottom of the tank over time. This build-up is called sediment and can be removed through regular cleaning to prevent it from affecting the water quality.

Rainwater Tanks: A Water Saver

From the roof to the tap a well-designed rainwater tank system can reduce your reliance on mains water and your water bills.

With the right filtration, treatment, and maintenance rainwater can be used for everything from garden irrigation to household drinking water. Using this natural resource is not only good for the environment but also self-sufficiency in water.