Why Harvest Rain Water? Calculate How Much You Can Harvest

There is nothing new about collecting rainwater. Storage jars used for water collection some 2000 years ago have been found as far away as Thailand .

rainwater tanksIn more recent times, we need to look closer to home to Spain and their Cisternas. All that has changed is an ever pressing need to help save our most precious resource and as a byproduct, save money. It is possible to save a substantial amount of water by the simple fitting of a rainwater tank or an above/below ground water storage tank.

This stored water can have a variety of uses from watering of your garden, washing of vehicles or to add to the mains water to your house, this however should be filtered.

Rain water is naturally devoid of minerals chlorine, fluoride and other chemicals and is better for plants, trees etc. It is surprising how much water can be collected from a standard roof , patio, driveway or any hard-standing surface around the home and then stored in water tanks. For every inch of water that falls on a surface of 1000 square feet it is possible to collect approximately 600 gallons of water .

It is a simple task to work out the rainfall on average for your area-:

Available rainfall

= Annual rainfall for your area (mm)** x Roof area (m2) x Evaporation Factor* x Filter Loss Factor*

* assumed as 0.9

** example rainfall


Typical 3 bedroom house (4 people), the yield would be;

800** x 120m2 x 0.9*x 0.9* = 77,760 litres

Expected usage

45% of 150 litre per person per day


150 x 4 x 365 x 45% = 98,550 litres

If you calculate 5% of the lower value, then a water tank size of 3,888 litres or one that is closest to that figure, would be the most suitable water tank size. One of the benefits of a modular system is that additional water tanks can be joined to the existing water tanks at a later date with ease.

If this water is put to use washing the car, watering the plants, washing the windows and even flushing the toilets, imagine the savings on water rates and the benefits to the environment. There are many methods of rainwater harvesting , rain barrels fitted to a downspout from a roof come in many shapes and sizes , some practical and some aesthetic. Thought should be given to sturdiness , child friendliness and safety, a cheap system will crack when the frosts come and would be a waste. Also run off of excess should be considered. Underground water tanks can store anything from 1000 litres to as much as 10,000. Although a common size would be 2800 litres. A special pump will deliver the water to a hose pipe on demand or to a header tank in the loft. A flotation valve automatically shuts off the pump if the tank is emptied. A soakaway system will remove excess water when full naturally into the water table. Apart from the above benefits there are others , less obvious:

» Eco rating points can be achieved

» Local planners are acting frequently more favourably towards eco-friendly schemes.

» The infinite benefits of washing your car during a hose-pipe ban quite legitimately, and the look on the neighbour’s faces!

Did you know?

German households use rain harvesting systems up to 300 % more than households in Ireland. However the use of these systems have increased by over 300 % in the last two years here.

Your typical rainharvesting system can yield up to 50 % of your water needs, a typical period for payback on a family with a high water demand is three years.

An average 4 bedroom family home roof can capture up to 100,000 litres of water each year, whereas a typical family’s consumption for standard use such as toilet flushing, garden watering , washing etc is 70,000 litres.

Source: Just Water Company (abbrev.)

There are son many good reasons to harvest rainwater, especially in a dry country like South Africa where water scarcity is a growing concern.  Ensure that high quality rain water tanks are used in your rainwater harvesting system.  JoJo Tanks offer high quality plastic water tanks that are available in an amazing diversity of shapes, sizes and colours.  All JoJo Tanks products carry a guarantee and the tanks are made from food grade plastic/polyethylene.  Click on the links below to view details of the various types and sizes of JoJo water tanks available in South Africa.

JoJo Tanks South Africa offer a wide range of plastic water tanks and chemical tanks to suit every household, business or agricultural need, including silo tanks and silo tank stands.  See JoJo Tanks VERTICAL TANKS, HORIZONTAL TANKS (transporter tanks), STEEL TANK STANDS and OTHER JOJO PRODUCTS. Also see JoJo Tanks’ NEW 6000 LITRE UNDERGROUND TANKS. Also see our FAQ and WATER TANK PRICES.

JoJo’s superior polyethylene plastic water tanks and steel water tank stands make JoJo Tanks the leaders in plastic water tank technology and the quality, affordability and guarantee on these water tanks make JoJo products the best choice in South Africa.  JoJo’s water tanks and chemical tanks come standard with a number of features that are often lacking on cheaper/inferior plastic tanks made by other companies in South Africa.

We are authorised JoJo Tanks dealers in South Africa and dispatch orders directly from JoJo Tank depots to save on transport costs. Full range of JoJo Tanks products and JoJo water tanks for sale.  CONTACT US for a quote on the right JoJo water tank or other JoJo product for you.  Special discounts are available on multiple orders of chemical tanks and water tanks and to our commercial and government customers.


(15000 litre and 20000 litre JoJo vertical water tanks also available on order)

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