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MMWD Blog: Think Blue Marin

Welcome to our blog! Written by staff at MMWD, “Think Blue Marin” explores all things water in south and central Marin—water supplies, conservation, new projects, watershed management, and more.

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Dec 06

Rainwater: What’s It Made of, and Why Is It so Good for the Garden?

Posted on December 6, 2016 at 2:24 PM by Ann Vallee

by Dan Carney, Water Conservation Manager

Marin is fortunate to have received 17.55 inches of rain at Lake Lagunitas since July 1—159% of average for this time of year and more rain is expected soon. Whether you like to sit and enjoy the sound of raindrops on the window, or splash in puddles, rain is good news for Marin. 

Rainwater is amazing stuff! According to researchers at the Scripps Institution of Oceanography, rain falling on the California coast is not pure H2O, but contains a mixture of particles including dust, carbon and nitrogen compounds, minerals, vegetative detritus and sea salt. It also has an average pH around 5.7, on the acidic side compared to pure H2O with a neutral pH of 7.0. But even with this mix of atmospheric particles, it is water of excellent quality.

What does this water chemistry mean for your landscape plants in Marin? The slightly acidic pH, low salt content, and dissolved nitrogen in rainwater create ideal conditions for making soil nutrients available to your plants. If you’ve ever noticed plants looking especially perky after a good rain, now you know why. 

How can you take full advantage of this liquid gold as it falls from the sky? The easiest way is to make sure that the rain falling on your property stays on your property. You can redirect roof drains into the landscape, create dry creek beds or rain gardens to encourage infiltration into the soil, and capture some of it in rain barrels to use on a sunny day. For more rainwater ideas, and to apply for a $50 rain barrel rebate, please visit MMWD’s Rainwater Harvesting webpage at


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