Rainwater harvesting can be described as the collecting of water that originates from rainfall. Every time the rain falls, you have a chance to harvest it. If harvested and stored correctly, the water can be of great use on commercial, residential or agricultural properties in South Africa.
The rainwater itself is normally relatively pure. This is due to the fact that it is formed after vapour evaporates from the ground and condenses in the atmosphere without particles or chemicals. Unless it is in places where the air is polluted badly.
Rainwater harvesting, therefore, majors on collecting the water that falls during rainfall before it touches the ground and becomes polluted by silt and other chemicals from the ground. The water is therefore relatively clean up until this point. This article is a guide to rainwater harvesting in South Africa.
Benefits of Rainwater Harvesting in South Africa
- Harvesting rainwater helps with controlling flooding.
- Reduces soil erosion in some areas.
- Gives people water living in areas which have no access to natural water sources.
- An adequate source of water for irrigating crops.
- Relatively cheap to install.
- Ends up reducing water bills.
- Helps solve drainage problems in towns and cities.
- Environmentally friendly.
Roof Top Rainwater Harvesting
The main method for harvesting water is “rooftop rainwater harvesting”. This is a simple cost-effective system of harvesting and storing rainwater. Here the rooftops act as the water catchment surface where the rainwater is collected. It is then directed to storage tanks or to artificial recharge systems. Rooftop rainwater harvesting systems include the following components:
- Rainwater harvesting catchment system
- The transportation system
- The First Flush System
- The Filter System
What is a Rainwater Catchment System?
The water catchment system is the surface upon which the rainwater falls before being redirected.
In this case, the water catchment surface is the rooftop. Rainfall falls on rooftops of residential and commercial buildings.
It then flows down to the gutters which then directs it to the necessary transportation systems attached.
In this case, the larger the surface area of the roof, the larger the amount of rainwater that will be collected within a given time period.
Rainwater Harvesting Transportation Systems
Water is normally transported through downpipes and drains from the roof. The best water pipes to use are those that are UV resistant; ISI HDPE and PVC pipes. The drains/pipes are normally fitted at the ends of gutters. They should be fitted with wire mesh to filter off the leaves and other substances that may have come down the roof with the rainwater.
First Flush Water Diverter System
This is a very critical component of the rainwater harvesting collection system. It determines the level of cleanliness of the collected water. The first flush is a device which ensures that the rainwater from the first rainfall that falls, after a long period without rain, is diverted away from the harvesting storage tanks.
When the first bit of rain lands on your roof, it will wash down all the dirt and debris that has been laying on your roof. This is the kind of water you are looking to avoid when rainwater harvesting in South Africa. Fitting a proper first flush water diverter is very important. It makes sure you get clean quality water. Water diverters enhance water quality. Reducing the need for regular tank cleaning due to contaminants from the rooftop.
The Primary Rooftop Flush
After it rains, water gradually fills up guttering framework before it moves through the downpipe. The first bit of water from the rooftop can contain a lot of microscopic organisms from decayed creepy crawlies, skinks, winged creatures and as well as droppings and concentrated tannic corrosives. Rather than streaming it directly to the water tank, these contaminators flows into the water diverter. The water diverter uses a ball and seat system – a straightforward programmed system that does not depend on mechanical parts or manual intercession.
How Does It Work?
As the water level ascents in the diverter chamber the ball drifts. Once the chamber is full, the ball lays on a seat inside the diverter chamber keeping any further water from entering the diverter. Any other rainwater that streams after this is then guided along the gutter pipe framework to the tank.
For water diverter to work properly, the polluted water that enters into the water diverter chamber must be closed off. This keeps the water from going to the storage tank. It guarantees that the contaminated water does not find its way into the rainwater harvesting storage tanks.
The system has a moderate discharge valve which guarantees that the chamber cleans itself after rain and resets itself.
Rainwater Harvesting Filtration System
Before the collected rainwater is stored, it needs to be filtered to remove particles and other contaminating components so that the stored water is clean and safe for use. Contaminants which the filtration system is set to remove from the water are:
- Volatile Organic Chemicals(VOCs) – These include things such as pesticides, herbicides among several other organic chemicals. Such chemicals are mostly in cities and town centres. If ingested in large quantities in water, they are known to cause liver, reproductive and kidney problems.
- Metal particles – As the water flows over the rooftops, it may carry with it some metal particles.
- Organic debris – There are also things like leaves or small twigs that may find their way into the collected rainwater and also small insects and they require to be filtered.
PVC Piping Used For Rainwater Harvesting System
There are different methods of filtration that can be used with your rainwater harvesting system. The diameter of the PVC pipe used can range from 1-1.2 meters depending on the surface area of the roof. The larger the surface area, the larger the diameter of the PVC pipe that should be used.
At both ends of the filter, the size of the PVC pipe is reduced to fit into the size of the transporting inlet and outlet pipes. This filter can be placed in a horizontal or vertical position in the system. After the water is filtered, it is then stored in either artificial recharging systems or rainwater storage tanks.
Different Types of Rainwater Storage Tanks
Another way that rainwater can be stored is by directing it into rainwater storage tanks. There are different types of water storage tanks that are used to store rainwater. These water tanks in South Africa come in a range of shapes and sizes.
#1 Polyethylene Rainwater Storage Tanks
These are tanks are made out of polyethylene. They are the most commonly used tanks, especially in residential, commercial and agricultural properties in South Africa. These water tanks are made locally by a few different suppliers.
These tanks are built strong and have been made to withstand temperature fluctuations and bad weather.
Polyethylene water tanks can also be used to store chemicals. They have been manufactured in South Africa to the strictest quality standards. This is to ensure the proper storage of chemicals can be achieved. They are also reasonably priced.
Polyethylene water tanks can be grouped into two major groups:
- Above-ground polyethylene tanks
- In-ground polyethylene tanks
Above-Ground Rain Water Storage Tanks
These are polyethylene tanks which are placed above the ground. They range from 300 litres to 20,000 litres in volume. They come in an array of shapes and sizes. Also known for their durability, lightweight and long-lasting characteristics. They can either be placed at the ground level or at a raised level like on top of buildings.
In-Ground Rain Water Storage Tanks
These are polyethylene tanks which are placed underground. Buried inside the ground. They have ribbed designs to increase their strength. They are a bit costly to set up due to the excavation charges.
#2 Galvanised Metal Rainwater Storage Tanks
These are normally made out of steel which is galvanised with zinc and the inside coated with a layer of a food-grade liner like PVC, epoxy paint or polyethylene.
They are usually a bit expensive. The galvanised tanks were created to prevent rusting in the old mild steel or iron tanks.
They are a little less durable since the galvanizing layer tends to wear out with time and the tanks do eventually start to rust.
These tanks can also be made to the size you need. Accessories can be bought like ladders to access the larger water tanks.
Something to take into consideration is that the larger the tank is, the heavier it is. The base structure would need to be solid on the bigger water tanks to hold the weight.
#3 Stone/Concrete Rainwater Storage Tanks
These are tanks which are made out of either pure concrete or a mixture of concrete and stones. They are usually constructed where large storage tanks are required. They are normally custom designed and built and can be built to any size. These tanks are more durable since they are not affected by weather. Also, they ensure that the water remains cool even in hot climates.
Another thing with these tanks is that they can either be constructed in-ground or above the ground. However, they are quite expensive to construct.
#4 Wooden Rainwater Storage Tanks
These are tanks made of wood/timber. They are not very common. They are mainly made of redwood, pine, cypress or cedar and rapped with steel tension cables for strength. The inside is then lined with an approved liner. The wood water storage tanks are visually appealing and they are mainly used for their aesthetic value.
#5 Fibreglass Rainwater Storage Tanks
These tanks are manufactured in standard capacities of 50 to 50,000 gallons. They can be either vertical cylinders or low-horizontal cylinders in configurations. These tanks can be used for potable water. Although they are primarily used in in-ground applications.
#6 Bladder/Pillow Rainwater Storage Tanks
These are collapsible rainwater tanks made of extra strong geotech fabric attached to a heavy gauge galvanized steel frame. The bladders are placed either under the house or deck. The rainwater from the rooftop is diverted through downpipes to a common in-flow pipe which then pours the water into the bladder.
To avoid overfilling and bursting of the bladders, when the bladders are full, the excess water is diverted to a stormwater collecting system. If there is enough space, several bladder tanks can be installed attached end-to-end or side-by-side to allow maximum rainwater storage.
Normally bladder tanks are designed to stretch to a maximum height of 600 millimetres. The bladders can easily be transported and they are a great choice for crawl spaces or outdoor locations like in construction sites.
#7 Onion /Pumpkin Rainwater Storage Tanks
These tanks are designed with open tops and self-rising tank walls. The main advantages of these tanks are that they can virtually be moved and set up in minutes. These are great tanks especially for military use or when hiking and people require to harvest and store rainwater.
#8 Folding Frame Rainwater Storage Tanks
These tanks are made with a strong outer frame as well as an interior liner. The interior liners are made from a wide range of fabrics. When it is not raining and the tank is empty, these collapsible tanks are folded flat and stored. When rain is anticipated, they are easy and quick to unfold and install.
Advantages of Rainwater Harvesting in Johannesburg, Pretoria, Durban and Cape Town
- Harvesting rainwater helps in flood control.
- Soil erosion is reduced in some areas.
- Gives people in rural areas access to water
- Can be used to water gardens.
- These systems are not expensive to install.
- Nice reduction in water bills.
- Solve drainage problems
Stormwater Collection Systems
Stormwater is different from rainwater. They both originate from rainfall. However, the stormwater is that water which has already reached the ground and it is normally contaminated with silt and other components found in the soil. There are various methods of collecting stormwater and storing it. Furthermore, it can be used at a later time instead of letting it to flow away on the ground and at times even cause damage in terms of erosion.
Methods of Collecting Stormwater
There are several methods of harvesting stormwater. Some of these methods are used to trap stormwater to enable it to infiltrate into the ground while some are used for storing the collected water for domestic and commercial use. Those methods which are used for collecting stormwater for domestic and commercial use have several stages which are:
Stormwater is harvested/collected from a drain. This is the rainwater which has reached the ground and it flows into the drains. The drains are usually placed in the subsurface and they help in collecting the rainwater that sips into the subsoil layer. The collected water is then temporarily stored in either underground or above-ground systems.
In the temporal storage systems, the collected stormwater is treated so that it can be safe for use. Filters and hydrodynamics separators are used. Filters help in removing things like phosphorus. There are several types of filters to consider when designing a stormwater filtration system. Hydrodynamic separators, on the other hand, are used for removing solids. It is a very effective way of removing large solids, debris and trash. After the water is treated and it is safe for use, it is then distributed to the various places where it is required to be used.
Stormwater Collection Methods
#1 Building Infiltration Trenches
Infiltration trenches are superficial excavations filled with homogeneously crushed stone to create underground reservoirs for stormwater or runoff. They are similar to soak pits. The walls and the top of the infiltration trenches are lined with geo-textile. This is to prevent sediment from penetrating into the trenches.
In other cases, the trenches are designed to include vegetative cover and other features, in an effort to make it a bio-filtration area. In most cases, these trenches are constructed next to outdoor parking lots or streets. The trapped stormwater then slowly infiltrates through the bottom of the infiltration trench into the subsoil layer and then gets into the water table.
#2 Constructing Grass Filter Stripes
Grass filter stripes also commonly known as filter stripes or grassed filters. They are usually thickly vegetated areas where surface flow from adjacent areas flows into. They help in slowing the speeds of runoff, providing a self-efficient way for the runoff to infiltrate the trapping sediment. These in most cases increases the fertility of the land.
#3 Construction of Pervious Pavements
These are permeable pavement surfaces with an underground stone reservoir. The stone reservoir stores the collected surface runoff for a short time before directing it to other drainage systems or storage systems. They are mainly used in town and cities where most of the ground is covered by pavements. These systems help in reducing flooding of towns and cities.
Above Ground Water Tanks in South Africa
There are different rainwater harvesting storage tank options. You can either get an above ground water tank installed or an underground water tank installed. Both of these two options come with advantages and disadvantages. In this section, we will do a comparison of the water tank options. One of the primary advantages of the above ground water tank is the fact that is the more cost-effective solution to get installed. This is because of the cost involved with digging the system into the ground. A DIY installation can also be done.
The above ground water tank might be cheaper to get installed, but you have to remember that they will be affected by the outdoor elements. If you live in a particularly cold climate you could have the water in the pipes freeze on you.
Another thing to take into consideration is the cleaning of the water tank. The above ground water tank is much easier to clean out because you have sufficient access to the tanks. Obviously, an underground water tank would be much harder to flush out and clean.
The above-ground water tanks in South Africa take up quite a lot of space around your home. Some homeowners might consider these tanks an eyesore.
Underground Water Tanks in South Africa
Underground water tanks are buried underground. It costs quite a bit more to get an underground water tank installed on your residential or commercial property in South Africa. This is because of the work involved with getting these huge water tanks buried underground.
One of the advantages of the underground water tank system is the fact that you can enjoy more space around your house and in the garden. They take up absolutely no space. The best time to get an underground water tank installed in South Africa is during the construction phase. It’s the most cost-effective way to go. A water pump is also required with this system. It pumps the water from your tank storage underground to the surface.
Finally, if you decide to get an underground water system installed in South Africa, make sure it has sufficient reinforcement. Remember you want the water tank to last for many years underground. Make sure your installers have handled the underground pressure problem. You don’t want to end up with cracks in your new rainwater harvesting storage tank system.