3 Must Know Facts about Rainwater Harvesting

Wondering whether rainwater harvesting is right for you? Here are 3 quick facts you should know…

Rainwater catchment is a crucial step towards making our cities more sustainable. In other parts of the world, it is well established as a system for water conservation. On the Central Coast of California, it is now gaining steam. Read on to learn 3 important facts that you should know about rainwater catchment…

1.You can get a lot of water, even if it doesn’t rain much…

We all know it doesn’t rain much on the Central Coast, but it does rain, right? In San Luis Obispo, for example, even in a dry year we can expect to get over 10 inches of rain.

When harvesting rainwater, for every inch it rains on a 1,000 square foot roof, you can collect 600 gallons of water.

This means that if you put a rainwater harvesting tank under the downspout of that 1,000 square foot roof, you could collect> 6,000 gallons of water with 10 inches of rain! That’s a lot!

In fact, when evaluating people’s homes for rainwater catchment, I most often find that the limiting factor is not the amount of rain we get, it’s the amount of space that is available for a rainwater tank. Most people can’t fit a 6,000 gallon tank in their yard!

Even if you can’t fit a huge tank in your yard, you’ll find that our rain patterns in San Luis Obispo county are well suited for rainwater catchment. We tend to get individual rain storms for a few days, then a couple weeks of dry weather. This means the rain storm will fill up your tank, which lets you use that water for irrigation, washing the car, or whatever you want in the dry period between storms. When it storms again, your tank gets refilled, and on and on. Using this method, many people can go all winter with using only rain for their outdoor water needs.

2.Rain tanks are clean…

“If I install a rainwater tank, will it become a become dirty, algae filled mosquito breeding ground?” This is a common concern I hear from people about rainwater tanks. Of course, it’s completely understandable to be worried about that. At first glance, it seems like rainwater tanks filled with standing water for weeks or months on end would be a terrible thing to keep in your yard.

Luckily, the people who designed rainwater tanks had this in mind when they were built. A proper tank will come with a mosquito screen that prevents them from entering or laying eggs in the tank. Assuming your rainwater system was properly installed, you should have no problems with mosquitoes.

The other good thing is that rainwater tanks are typically installed in such a way as to minimize or eliminate light entering the tank. Without light, there is no photosynthesis, and thus no algae.
You can keep your tank even cleaner by installing a first flush diverter. The “first flush” is the first flow of rain that comes off the roof after a dry period. This is the water that contains the majority of debris and particles that you may want to keep out of your rain tank.

By using a well-made rain barrel and using proper installation practices, you won’t have to worry about dirty tanks or mosquitoes.

3.You can capture rainwater in your landscaping…

You don’t even need a tank to harvest rainwater, you can use your yard! Plus, it’s often easier than you might think.

To do this, you need to dig out a swale, or catchment basin, in your landscaping and divert your downspout into the swale. The swale is shaped to slow the rainwater as it flows and allow it to permeate into the soil.

This can dramatically reduce the amount of supplemental irrigation that you need, while also allowing the soil to naturally filter out pollutants that build up on your roof, which keeps our waterways and the ocean cleaner.
Capturing rain in your landscaping is referred to as passive rainwater catchment, or a rain garden. Rain gardens are beautiful, functional, and have huge benefits for our natural environment.


Rainwater harvesting is on the rise in San Luis Obispo county. Some cities, such as Cambria, are well ahead of the curve and have a large amount of catchment systems already. If you are in SLO county and need help with your rainwater harvesting system, don’t hesitate to give us a call. Water conservation is what we’re all about at Greener Environments, so we’d love to help!