Monterey Rainwater



rainwater catchmentRainwater Harvesting Frequently Asked Questions

1. How do you harvest the rain?
2. What is the problem with rain barrels? 
3. What is the most cost effective way of harvesting rain?
4. Why is rainwater harvesting especially important for Carmel Valley and Monterey?
5. Do I need pumps to harvest rainwater?
6. Does drip irrigation or soaker hoses, work with a rainwater?
7. How big of a property can I water? 
8. What is a first flush device? Do they help? 
9. What type of piping is best?
10. Can I water my lawn with rainwater? 
11. Is the water quality a problem in rainwater systems, and how can I collect cleaner water? 
12. Is rainwater harvesting suitable for commercial as well as at residential? 
Are there any current rebates?
14.What kind of roof is best to harvest rain? 
Where does the .623 number come from when calculating how much rain I can harvest? 
What is potable water? 
17. What are LEED points? 
18. Who should install a Rainwater Harvesting system? 
20. Are there difference is roof efficiencies in capturing rain? 
21. How much rainwater should I harvest?


  • 1. How do you harvest rainwater?

    The process of harvesting rainwater is really quite simple. The rain hits your roof, is collected by the gutters, and then instead of been disposed of through the downspouts and wasted, the rainwater is diverted to a storage tank. While it's being collected, it’s run through a number of screens and also being further cleaned by what's known as a first flush device.  Gravity is very important because it is the driving force of this initial collection process.  If the tank can be situated below the gutter than this process remains quite simple, but this is rare and most people don't want a big tank adjacent to their home, if the tank is set  further away, and up above, or near the height of the gutter,  than a pump is used.  With this design, the rain is collected in a small tank near the house, below the gutter, and then the pump sends the water across the property, and uphill into the storage tank.  This pump has a dual purpose in that it also distributes the water.  So a proper pump is desirable anyway  This system has shown itself to be very useful in collecting a lot of water, and keeping the storage tanks away from the house where they are more easily hidden.

    2. What is the problem with rain barrels?

    The problem with rain barrels is that they just don't work.  Any decent sized property will need at least 50 gallons a day to irrigate their landscaping.  This needs to cover the dry season from July through September. So 100 days at 50 gallons a day is 5000 gallons. Rain barrels are usually about 55 gallons; this means you would need a hundred rain barrels to properly care for your property. They’re a Band-Aid when you desperately need a tourniquet.

    Many people in the business are happy to sell Rain barrels. The hope is that you'll enjoy collecting rainwater for the season,  realize that you need more storage, and then come back to them and buy the size system that you needed in the first place.   It’s B.S. Not only does this mean that you miss out on a full season of irrigation, but you end up with just another pile of wasted plastic, that needs to be disposed of.

    So, with our situation here on the Monterey Peninsula it's all about storage. More than enough rain hits our roofs (about 10,000 gallons per roof) we just need a place to put it all. So rather than catch 55 gallons of rain in February and using it in one day in September, what you need to do is get used to the idea of having a least one large tank stashed somewhere on your property. I know this hard part to swallow, but these tanks can be easily disguised with some fencing or even plants supported with trellises. They can even be creatively painted to blend in. In the end, if the tank is the driving force that keeps your yard alive than the space that the tanks use up is very well used.

    3. What is the best way of harvesting rain?

    Right off the roof, and into a plastic tank.  Slate and tile roofs are best but composition roofs work very well too.  There is a little loss with wood roofs but we usually get enough rain for them to work just fine.

    4. Why should I harvest rainwater?

    As far as water is concerned, the Monterey area is an island.  We're disconnected from the rest of the state, and must rely on our own very small watershed.  This means we must take more extreme measures to manage our water needs.  This problem gets worse and worse as the public water system fails to provide what it can.   The water situation here is going to get worse before it gets better, perhaps much worse.   I’m starting to realize that there is a method to their madness.  The worse things get and the more desal plans that fall apart, and the closer our deadline from the state to quit over drafting the Carmel river, the more we a forced to accept whatever Cal-Am offers us.  I believe that by the time our water issues are settled we we have to most expensive water in the country.   This means the homeowner needs to provide as much of their own water as they can. Rainwater harvesting does just that.  Greywater too!

    5. Do I need a pump to harvest rainwater?

    It depends on the lay of your land.  If your tank is below your gutters and your landscaping is below your tank then a gravity tank can work for orchards and larger plants.   If the water needs to go through irrigation piping then a pump is need so the water can mimic the pressure the system was designed for.  There are some great pumps, made specifically for this purpose.

    6. Can I use drip irrigation or soaker hoses with a rainwater?

    Yes The trick to using drip irrigation systems is to make sure that the system is design to clean the collected water so it is as free as debris as possible. Also an inexpensive filter is installed before the water goes into your irrigation system

    7. How big a property can I water?

    It all depends on the size of your roof and how much storage you can install.  So far I've been working with larger properties of about 2 to 4 acres.  Many factors come into play.  Is the property in the valley or by the coast? Are low water use plants used in the landscaping?  Even being on the cooler north side or hotter south side makes a difference.

    8. What is a First Flush device?

    A first flush device is a product that allows the initial flow of water off the roof to be diverted directly to the storm drain. The initial flow draining off of a previously dry roof can contain impurities that should not end up in the tank. Most of our diverters incorporate a first flush action. This ensures that the initial flow passes to the storm drain. Since our diverters incorporate this technology, a separate device that requires maintenance is not needed with one of our systems.

    9. What type of piping do you use?

    We try to use the best piping for each situation which means it changes often.  PVC  for strength going into the tank, ABS for collection and overflows, and my favorite is using the low environmental PE piping whenever possible..

    10. Can I water my lawn with rainwater?

    Yes, but a lawn usually takes a lot of water. A typical lawn requires about 3,000 gallons a month.

    Before going with big tanks to water your lawn you  should look at changing at least part of your lawn to local vegetation, drought hearty plants and  installing either drip irrigation or soaker hose will reduce your water consumption.

    11. Is water quality a problem in rainwater systems?

     Rain water is generally free of harmful minerals and in most cases chemicals, but can be contaminated by animals in the catchment area. Rainwater for drinking should be carefully stored and treated prior to consumption. Several technologies exist for home treatment including: UV, ozone sterilization, chlorination and distillation.

    12. Is rainwater harvesting suitable for work as well as at home?

    Yes!  Rainwater catchment is very well suited for commercial applications.  The catchment areas ( the roofs) are larger, and commercial  operations  are often able to use their rainwater  all winter long.  This allows their systems to be refilled many times in one season, multiplying the amount of water they can collect many times.  Also businesses tend to have more uses for non-potable water  than the most residences.

    13. Are there any rebates?

    The water district has offers very generous rebates of $50 for every hundred gallons of storage  up to the first 500 gallons.  Then they pay $25 per hundred gallons of storage up to 25,000 gallons.  This usually comes to about 60%  of the most expensive part of your water system, the tanks.

    14. What kind of roof can be used to harvest rain?

    Rainwater can be harvested from any roof; however, some roof materials present health risks if the water will come into significant human contact. Copper roofs leach copper into the water and old copper roofs may contain lead solder. For these reasons, rainwater harvested from copper roofs 
    should not be used for potable uses or in fruit/vegetable gardens. 
    Asphalt shingle roofs, cedar shingle and similar types may leach 
    some materials in the first year of use that can be harmful for 
    human consumption. The Virginia Rainwater Harvesting Manual and the 
    Texas Manual on Rainwater Harvesting both provide additional 
    guidance on roofing material

     15. Where does the .623 number come from when calculating how much rain I can capture?

    16. What is potable water?

    Potable water is another name for fresh drinking water. Water of sufficient quality to serve as drinking water is often calledpotable water.

    17. What is LEED? 
    LEED stands for Leadership in Energy and Environmental Design. It is a ranking system; whereby, buildings can be evaluated on a specific set of criteria against other buildings. The result is a set of points that rank a building's "sustainability". Water conservation is one of the ranking categories in the LEED evaluation process. To read an article on water and LEED.

    18. Who should install a Rainwater Harvesting system? 

      Someone trained specifically to understand the many nuances of collecting rainwater, but also has experience working on  properties and understands the special needs of this area.

    20. Are there differences in the efficiency of roof materials in capturing rainwater?

    Yes, below is a table listing the differences.

    ·  < efficiency runoff 95% a assume roof metal tile For align="left">

    ·  For a concrete/asphalt roof assume a 95% runoff efficiency

    ·  For a gravel roof assume a 70% runoff efficiency

    ·  For a bare soil roof assume a 75% runoff efficiency

    ·  For a grass roof assume a 17% runoff efficiency

    21. How much rainwater should I harvest?

    The short answer is how much do you need. Then there are various methods determine this amount. The easiest is past water bills. If inside and outside this, average the water bills to determine what your monthly average would be. If outside then it largely depends on square footage landscaped, where you live and what you are watering. Some very rough, but simple guidelines are:

    Daily Consumption

    ·  Per Person 50 -100 gallons

    ·  Gardens/Lawns 600 gallons per 1,000 square feet

    ·  Young Trees 15 gallons

    ·  Small Animals .25 gallons per 25 pounds

    ·  Dairy Cattle 20 gallons

    ·  Range Cattle 15 gallons