A circular plastic

“rain-catcher”

Peter Morgan 2016

2

Introduction

The rain that falls on the Earth is the source of most of the freshwater we drink and is

used in most aspects of our daily lives. Much of it enters the ground to form the huge

underground water storage reservoir in aquifers. More drains into rivers and streams

where it may fill lakes, dams and reservoirs, both natural and man-made. Some of it

may be trapped by various rainwater harvesting techniques and stored in water storage

tanks and containers and tanks. Much has been published on this important subject.

In an earlier work written by Aquamor (which can be viewed on the Aquamor website -

www.aquamor.info), the use of portable, plastic rain-catchers was described and how

the water could be managed and stored in specific tanks to improve water quality

(Rainwater harvesting in the homestead. February 2015). This system used UV

resistant plastic sheet as the rain-collector, which could be stored out of harm’s way, but

quickly installed on permanently mounted supports when the rains are close.

This manual extends this concept by using a circular plastic sheet, supported by a ring

of PVC pipe and directing the water into a suitable container. In this case the rain

collector is also portable, but can be hung by wires from objects like trees which are

permanently sited in the garden. In the case described here, the unit was initially

suspended from the branches of trees to collect rain water for gardening purposes. It

was later mounted on poles, which made the unit more stable..

It is well known that natural rainwater is superior in its quality when compared to

underground water (or tap-water) for the irrigation of plants. It has a more neutral pH

than many ground waters, less chemicals than tap water and also by passing through the

atmosphere the rain water picks up vital nitrogen which can be easily absorbed by

plants and is essential for healthy plant growth. That is why we see rapid growth in our

garden following the rains, even after parts have been watered with ground water

before. In this case the rainwater is used to irrigate special crops like sweet potato,

grown in special boxes, bags and jars to enhance growth and productivity. Rainwater

used for gardening can of course be collected from the house roof, but in this case the

rain catcher is portable and can be located in any suitable area of the garden.

The collection, storage and use of rainwater is an important homestead activity that can

benefit any family. A unit similar to the one described here could be used to collect

water for domestic use, but it should be mounted in the open away from trees.

Permanently mounted treated poles will serve the purpose. The earlier work mentioned

above describes this in more detail for larger plastic rain catchers.

Rainwater is precious

Peter Morgan

Harare

February 2016

3

Construction

The rain catcher is made from a combination of PVC pipe and plastic sheet, in this case

a 6m length of 25mm PVC pipe was purchased and some thick black plastic sheet. In

this case the 6m length was cut up into 3 pieces to make it easier to transport. The

pieces were cemented together again using strong PVC connectors to reform the 6m

length. Reconnecting is also possible using short lengths of slightly larger pipe and

connecting the smaller pipes within the larger pipe and holding tight with strong tape.

The ideal is to use a full 6m length of 25mm PVC pipe with one end opened up as a

socket (this is how it is sold) – and simply cementing one end into the other.

For this size of rain-catcher a sheet of thick black plastic sheet was used measuring 2m

x 2m. Note that the PVC piping could have been made in the form of a square or

rectangle using PVC elbows as joints at each corner. This round configuration was

chosen because it was thought to be more stable once formed.

A 6m length of 25mm (class ) PVC pipe is taken and made into a circle.

A 2m x 2m sheet of thick black plastic is taken and laid under the PVC ring. It is then cut

slightly larger than the ring. The cuttings taken off from the corners of the plastic sheet were

then recut to form segments which were glued with contact adhesive around the rim of the

plastic disc to strengthen the sheet at the edges.

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The rim of the plastic sheet was then attached to the PVC ring by using a series of stitches made

with strong twine. These held the plastic to the PVC ring securely.

The water outlet system

A water outlet system is fitted in the middle of the plastic sheet to allow captured water

to escape through a downpipe into the water storage vessel. This was made from a

plastic jam jar with a screw top lid.

Plastic jam jars are common in Zimbabwe. A hole was cut in the lid as shown above. A hole was

cut in the base of the plastic jam jar to suit the size of a 25mm plastic poly-pipe fitting. The

25mm poly-pipe fitting was secured within the hole made at the base of the jar with a mix of

“Pratley’s white” a hard setting bonding material.

The lid was mounted in the middle of the plastic sheet and a matching hole made in the sheet.

The upper surface of the sheet and the inner surface of the lid were then coated with contact

adhesive and then (after a few minutes) bonded together. The jar with its course thread was then

screwed into the lid bonded to the plastic sheet.

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Fitting a screen and mounting the circular rain catcher.

In order to stop leaves and insects and other debris passing into the water containers a circular

disc of stainless steel screen was bonded to the top of the jam jar lid. Initially the rain-catcher

was then slung from the tree branches so that it was stable and laid in a horizontal position.

Each supporting wire is attached to the rim of the rain catcher (the PVC loop) and then, above,

to a branch of a tree. Alternatively the supporting wires can be attached to poles mounted in the

ground around the rain-catcher. For collecting domestic water the rain catcher should be sited

in the open and not under trees and supported by poles mounted in the ground.

The wires were adjusted so the water gravitated into the centre of the sheet around the jam jar

lid. The 25mm plastic pipe draining water from the collector can be directed straight into a

smaller (25li) plastic container. But it is more convenient to director the water through an elbow

to a larger container, such as a new or unused plastic dustbin, as shown here. Rain water can

then be decanted from the dustbin as required.

A hole is cut into the side of the dustbin and a 25mm poly-pipe connected fitted through it and

secure with a hard setting adhesive like Pratley’s white.

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Mounting on poles

The same collector can be mounted on poles and used to collect water for domestic use,

but it must not be placed under trees, and mounted in a position where it can be

regularly cleaned and flushed. The poles should be treated against termite attach. The

rain collector is attached to the poles with wires which can easily be detached so that

the collector can be thoroughly cleaned or stored out of the sun during the dry season.

The “Rain Catcher” mounted on poles and 25li plastic containers used to store the water.

A funnel is used to decant water from the 90li bin into the 25li containers.

Amount of water collected

This collector is small compared to a roof, but it is simple and can be replicated. The

collector shown here has a rain catching diameter of 1.7m and thus a surface area of

2.26sq.m. In approximate terms one mm of rain falling on one square metre of

rainwater collector surface will yield one litre of water. Thus 1mm of rain falling on this

collector will yield approximately 2.26litres of water. A downpour of 20mm will yield

about 22 litres. If the annual rainfall is 500mm the total yield could be 1.1cu.m. But this

is approximate as some rainfall is always lost. Larger plastic rain catchers, which collect

far more water have been described early by Aquamor.

Rainwater passing into the storage bin. It is then decanted into 25li containers or a watering can.

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Initial showers

A circular concrete disc was made and placed around the jam jar lid to act as a weight to lower

the centre of the sheet. This also held back larger leaves falling from the tree above. This water

then flowed into the rainwater collector, in this case a plastic dustbin, but in other countries

called a water butt. Water for storage was decanted into 25li plastic containers. For immediate

use on the garden the collected rainwater was decanted with a scoop into a watering can and

then used to water special crops and beds.

Using rainwater to irrigate a special bed of sweet potato. In this case the bed is raised off the

ground on a plastic sheet and the raised “box” is made of bricks. The “box” (or “raised ring

beam”) has been filled with mix of garden and leaf compost, which provides a rich and loose

medium in which the plants can grow. This photo was taken a day after the sweet potato slips

and sprouts taken from last year’s growth, were planted. Sweet potato is a nutritious and

valuable food crop, often grown traditionally together with the maize. In this case the bed has

been prepared in the hope of getting a good harvest. Time will tell.

The sweet potato after a month’s growth.