I'm Gwen Outen with the VOA Special English Agriculture Report.

When we think of harvests, we usually think of plants. But can you also harvest a liquid? Sure. Just think of rainwater. Best of all, it is free, except for the cost of a way to collect it.

One way to harvest rainwater is with some technology developed by International Development Enterprises. This is a non-governmental organization. It is based in the American state of Colorado. It created the technology as a way for people in developing countries to avoid having to drink polluted ground water.

The rainwater harvesting system created by International Development Enterprises uses pipes to collect water from the roofs of buildings. The pipes stretch from the buildings to a two-meter tall storage tank. This tank is made of metal. At the top of the tank is a so-called "first-flush" device made of wire screen. This acts as a barrier. It prevents dirt and leaves in the water from falling inside the tank.

A fitted cover sits over the first-flush device. It protects the water inside the tank from evaporating. The cover also prevents mosquitoes from flying into the water and laying eggs.

Inside the tank is a low-cost plastic bag that collects the water. The bag sits inside another plastic bag similar to those used to hold grain. The two bags are supported inside the metal tank. In all, the water storage system can hold up to 3500 liters of water.

International Development Enterprises says the inner bags may need to be replaced every two to three years. However, if the bags are not damaged by sunlight, they could last even longer.

International Development Enterprises says the rainwater harvesting system should be built on a raised structure. Doing so will prevent insects from eating into it from the bottom.

The developers say one tank can provide a family of five with enough rainwater to go through a five-month dry season.

Internet users can get more information about International Development Enterprises at its Web site: ideorg.org. Again, the spelling is i-d-e-o-r-g dot o-r-g.

We'll have a link on our Web site, where you can read and listen to our programs. That address is voaspecialenglish.com. And, if you have a question or comment, write to special@voanews.com.

This VOA Special English Agriculture Report was written by Jill Moss. I'm Gwen Outen.  

fitted: 合身的，按实物尺寸做的

evaporate: to convert or change into a vapor（使蒸发，使变为气体）