It’s legal to collect rainwater off of a roof for beneficial use and doesn’t require a water rights permit in California. Rainwater is renewable, clean, soft water with the perfect ph for cannabis cultivation.
It’s been completely legal in California to collect rainwater off of a building roof since the AB-1750 Rainwater Capture Act of 2012 came into fruition. On top of this progressive statute, California recently passed the California Proposition 72, Rainwater Capture Systems Excluded from Property Tax Assessments Amendment.
This amendment excludes rainwater systems from property tax reassessment, starting January 1, 2019. For cannabis cultivators, these initiatives extend in making permitting easier when your water source is rainwater collection.
Unlike with surface water diversion, or water wells, rainwater collection for cannabis doesn’t require a water rights permit. You just need a rainwater system that can supply enough water for the cultivation production that you are applying for.
“Rainwater catchment systems collect runoff from rooftops which are then stored for later use. Since collecting rainwater in this way does not require additional state permitting, it is a cost-effective solution to meeting some of your water needs.” – The Humboldt County Planning and Building Department (Link)
The first step to rainwater collection is to test the rainwater runoff from the building gutter system, especially when used for drinking or irrigation for your cash crop. There are testing kits like WaterSafe (https://www.watersafetestkits.com/) or testing facilities (https://www.calwater.com/waterquality/water-quality-testing-labs/) that can provide contamination information.
The quality of the rainwater depends on the roofing material, and location of your system. Typical rainwater systems include pre-tank filtration as well as more filtration before the rainwater is used.
Using rainwater for cannabis (or growing in general) has many advantages, besides easier permitting.
1. Rainwater is soft water. It’s free of the salts, minerals, treatment chemicals, and pharmaceuticals that are found in municipal water, groundwater, and surface water. Salts and chemicals can build up in your soil over time and these residues are tough on plants.
2. Rainwater has a slightly acidic ph. Organically grown plants prefer soil pH levels between 5.5 and 6.5. This is on the acidic side of the neutral pH 7, and by nature’s design, it is the exact pH range for rainwater.
3. Rain contains nitrates, an important macronutrient. Nitrates are the most bioavailable form of nitrogen. Nitrogen is one of the three key macro-nutrients that plants need to thrive.
4. Collecting rainwater off of a building roof is renewable, reduces the distance between the source of your water and use, and is proven to reduce stress on groundwater resources.
Some growers have noted that they sometimes need to add minerals to filtered rainwater, but it depends on your specific setup, system and watering needs. Water is one of the most important factors when it comes to growing cannabis successfully so testing is necessary to ensure the biggest buds.
California Proposition 72, Rainwater Capture Systems Excluded from Property Tax Assessments Amendment (June 2018)
The State of California AB-1750 Rainwater Capture Act of 2012
The City of San Francisco Guide to Rainwater Harvesting
Truly Organic “Water Quality and Cannabis”
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