In the interest of water preservation, and the hope there will be demand for such a system one day, I shall lay down some important points to follow when designing a rainwater harvesting system. Also, for portable water harvesting portable systems, there's an active quest you might know about.

 

???? Why harvest rainwater?

Rainwater is valued for its purity and softness. It has a nearly neutral pH, and is free from disinfection by-products, salts, minerals, and other natural and man-made contaminants. It must be treated, however, to kill microorganisms and some chemicals.

???? What are the components of a rainwater harvesting system?

A catchment surface (like the roof or, in the case of a portable system, an umbrella) , gutters and downspouts; leaf screens/first-flush diverters (components which remove debris and dust from the captured rainwater before it goes to the tank) and one or more storage tanks/ cisterns.

???? What materials are needed?

A roof can be made of metal (55% aluminium/45% zinc alloy steel sheet), clay (painted with special sealant to prevent bacteria growth on porous surfaces), asphalt (not recommended), slate or wood/gravel (suitable for irrigation water).

The most common materials for gutters and downspouts are half-round PVC, vinyl, pipe, seamless aluminum, and galvanized steel.

The funnel-type downspout filter is made of PVC or galvanized steel fitted with a stainless steel or brass screen. Filter socks of nylon mesh can be installed on the PVC pipe at the tank inflow. You may experiment with leaf screens, but remember they need constant cleaning.

Storage tanks must be opaque, either upon purchase or painted later, to inhibit algae growth, and should be protected from direct sunlight, if possible. They’re made of fiberglass, polypropylene, wood (pine, cedar or cypress), concrete, metal, ferrocement.

 

 

Part II:

???? Filtering seems important. How can you achieve this?

Here are two images showing a filtering pipe and a filtering box:

Filters must be cleaned permanently, else they won't...well, filter. They can also become breeding grounds for pathogens. 

???? Why treat rainwater? Isn't it supposed to be purer than water?

As a raindrop falls and comes in contact with the atmosphere, it dissolves naturally occurring carbon dioxide to form a weak acid. The resultant pH is about 5.7, whereas a pH of 7.0 is neutral. Also, fine particulates can be emitted by industrial and residential combustion, vehicle exhaust, agricultural controlled burns, and sandstorms. As rainwater falls through the atmosphere, it can incorporate these contaminants.

???? How to treat rainwater, then?

There are a number of possibilities, but two simple methods should be talked about: boiling water and...letting it in the sun? The UV light kills more microorganisms than you'd think.