Help Me With...

Select from list
My Residential Property
My Driver's License or Vehicle Registration
Requesting Assistance
Health Department


Select from list
My Property Valuation
Understanding My Valuation
Paying My Property Tax
Neighborhood Sales
Building Permits
Vehicle Registration - New Stickers
Vehicle Registration - New Vehicle
Drivers License - New or Renew
New Resident Vehicle Registration
Adult Protection
Child Welfare
Child Support
Child Care
Financial Assistance
Medical Assistance
Food Assistance
Register to Vote / Update Voter Registration
Upcoming Election Information
Ballot Drop Box Locations
Voter Service and Polling Centers
Birth/Death Records
Restaurant Inspections
Community Health
Child Care Center Inspections
Septic System Inspections
Emergency Preparedness & Response
Disease Surveillance
Mental and Behavioral Health Education
Community Health and Clinical Services
Women, Infants and Children


× Close

Rainwater Harvesting

Subscribe to receive RainWater Harvesting updates or future workshops.

Click here

Rainwater collection, also called rainwater “harvesting,” is the process of capturing, storing, and directing rainwater runoff and putting it to use. Water from roof gutter downspouts is usually directed onto landscaped areas and is incidentally consumed by plants, but this form of use is not regarded as rainwater harvesting.

Actual rainwater harvesting involves the collection of rainfall runoff from rooftops, concrete patios, driveways, and other impervious surfaces. Rainwater collection systems vary from simple and inexpensive to complex and costly. Typically, rooftop rainwater collection systems are simple, consisting of gutters, downspouts, and storage containers. Inexpensive rainwater storage systems commonly make use of an above-ground container such as a barrel or plastic tank with a lid to reduce evaporation and bar access for mosquitos to breed. Any container capable of collecting the rain shedding from a roof or patio can be used as a rainwater harvesting system, but to be in conformance with Colorado water law, the container additionally must be equipped with a sealable lid. More sophisticated systems have “first flush” diverters that are recommended to exclude capture of the initial rain that might carry impurities from the roof.

Colorado residents should understand that water rights in Colorado are unique compared to other parts of the country. The use of water in this state and other Western states is governed by what is known as the prior appropriation doctrine. This doctrine of water allocation controls who uses water, how much water may be used, the types of uses allowed, and when those waters can be used. A simplified way to explain this system is often called the priority system or “first in time, first in right.” It may seem strange that rainwater harvesting in Colorado is so carefully watched, but understanding why this is so can provide valuable insight into the way water is shared in Colorado. In our arid environment, every drop counts, and water rights holders depend upon the runoff from snowmelt and rainfall to supply the beneficial uses to which they apply their water rights. Captured precipitation consumed “out of priority” may deprive downstream and senior water rights holders of their right to use water from the natural stream, which comprises water that originates as snow and rain. Even though the detention of rooftop precipitation might only be temporary and minimal, it may still alter the nature of historic flow patterns.  More information can be found on the Colorado Division of Water Resources per C.R.S. 37-96.5-102 and 103.

Read More

Benefits of Rainwater

Most homeowners in Colorado are now allowed to use rain barrels to collect rainwater.

A maximum of two rain barrels with a combined storage of 110 gallons or less are allowed at each household.

Collected rainwater may be used to irrigate outdoor lawns, plants, or gardens.   Untreated rainwater collected
from roofs is not safe to drink.

Frequently Asked Questions

What are basic system components I will need for my rain barrel?

Catchment Area

The catchment area is the first point of contact for the rain—generally the roof.  If you are planning to use your collected rainwater for landscape purposes, typical asphalt shingles are fine.  Wood shingles may contain preservatives that may be harmful to human health and metal roofs tend to shed contaminants.

The size of the roof determines how much water you will be able to harvest Area of roof (feet squared) x rainfall depth (inches) x 0.63 = Harvested Water in gallons.


40 feet long by 20 feet wide = 800 square feet of roof / 800 x 0.5 x 0.63 = 252 gallons when it rains ½ inch / 800 x 0.1 x 0.63 = 50 gallons when it rains 1/10 inch = Over the course of year = 1000 gallons!


Blue plastic rain barrel connect to downspout outside of homeThis is where you will divert and store harvested rainwater (your barrel!)  Safety is a concern with the storage vessel. It should be secure and clean, and follow all guidelines laid out in House Bill 16-1005.

Always use good safety practices when installing or making your rain barrel, and when using power tools. You might be able to find cheap barrels from bottling companies, bakeries, delis, feed stores, and other bulk food service places. You could also use a large trash can with a sealable lid.  Pre-manufactured barrels can be ordered online or purchased through hardware stores.


HB 16-1005 requires storage vessels to have a sealable lid.  You can cut a hole in the lid and attach a fine screen for a mosquito-proof inlet or cut many holes in the lid and attach a larger piece of screen.

Another option would be to have your inlet go in the side of the barrel, near the top.  The barrel should have an overflow outlet, an inlet for the downspout, and one to two hose spigots (at 3-4 inches from the bottom of the barrel to avoid sediment).


rain barrel elevated on bricksGravity Fed System – Overhead watering will be impossible due to inadequate pressure.  A drip system can work if the barrel sits 3-4’ above the emitters, but the flow will be very poor.  A very simple method is to set the hose near the base of the plants to be watered and move it every few minutes so you can fill watering cans with a hose.  Pressure will be best when the barrel is full and elevated.

Choosing a site

The area where the barrel is sitting should be sturdy.  A full barrel weighs around 400 pounds, so make sure it is secure! Concrete blocks can be used to make an area sturdier, which will also raise the barrel and increase the pressure.  Consider the length of the hose you will be using, and how far your barrel is from your landscape.


Select a downspout. You may need to cut your downspout to accommodate your barrel. Some things you may need when installing and/or making your barrel:

  • barrel with lid
  • safety glasses
  • drill
  • brass spigots (3/4 inch pipe thread and 1″ hose fitting is standard)
  • overflow adapter with either pipe threading or hose fitting
  • lock nuts
  • rubber washers
  • Teflon tape
  • silicon sealant
  • wrench
  • gloves
  • 15/16ths inch paddle bit
  • utility knife
  • fine screen for the lid and maybe soldering iron
  • steel wool
  • concrete blocks
  • tin snips or hacksaw
  • gutter elbow or flexible elbow


Elevate the rain barrel. Water flow increases when the barrel is elevated. And, it’s MUCH easier to connect your hose.  Install attachment for downspout for filtration.

What is a rain barrel, and how can I use one legally?

White plastic rain barrel on outside of home“Rain barrel” means a storage container with a sealable lid that is:

  • Located above ground outside of a residential home.
  • Used for collecting precipitation from a downspout or a rooftop.

Using a rain barrel per Colorado HB 16-1005:

  • Allows up to two rain barrels with a combined storage of no more than 110 gallons.
  • Allows any single-family residence, or multi-family units with 4 or fewer units, to collect from the roof.
    • “Single-family residence” means a private residence that is a separate building or an individual residence that is part of a row of residences joined by common sidewalls.
    • Townhomes: 110 gallons per residence.
    • Apartments/Condos (4 units or less) – 110 gallons per building (not unit)
    • Water MUST be used on the SAME PROPERTY that it is collected on.
    • Must be used OUTSIDE.

Can Homeowners' Associations (HOAs) prevent rain barrels?

The answer is no. Section 3 of Colorado HB 16-005 prevents an HOA from prohibiting a unit owner from using rain barrels for precipitation collection. However, an HOA can regulate where you put it and/or how it looks or is screened.

How can I use the collected rainwater?

Man filling up watering can from rain barrel catchment systemThe collected precipitation is used for outdoor purposes including irrigation of lawns and gardens.

Please note:  A person shall not use precipitation collected under this article for drinking water or indoor household purposes.

How much of an effect will a rain barrel make in my outdoor watering?

The benefit of a rain barrel is the ability to control the application of the harvested water — you can use it when you want to and where you want to.

How much money/water will I save with a rain barrel?

It depends on several factors, including:

  • Total precipitation
  • Hydrology
  • Landscaping features
  • Water-use of plants
  • Size of lot


What size area will 110 gallons cover?

You can adequately water (with ~1”) approximately 180 square feet (slightly smaller than a 15 x 15-foot area).

How long can I safety store rainwater?

Rain barrels are only ecologically relevant if you USE them.

It is ideal to use your collected rainwater within a week. Research has shown that it is acceptable to store rainwater for up to a month, however, if held longer, you should drain it.

During winter, you should disconnect your barrel, dry it, and store it upside down with the spigot open.

What about rainwater and mosquitoes?

rain barrel downspout into mosquito screenHouse Bill 16-1005 requires rain barrels to have a sealable lid.

In urban areas, mosquitoes tend to breed anywhere that holds and stores water for at least a week, and mosquito larvae and pupae live in standing water.

You should cover the inlet from the downspout into the barrel with a fine screen to keep mosquitoes from entering and completely empty the barrel at least once per month to prevent any mosquitoes that may have found their way in from breeding.

Your overflow hose should be at least 8 feet, this will prevent mosquitoes searching for water from finding your barrel. You can also attach a piece of screen to the hose adapter.

You may also buy mosquito dunks. The dunks contain a naturally occurring soil bacteria (Bacillus thuringiensis israelensis (Bti)) that is ingested by larvae and kills them.

What about water quality of rainwater?

Relatively speaking, rainwater in Colorado is generally of good quality.

One of the biggest problems here is that rain is infrequent, which leaves a lot of time for bird droppings, dust, and other contaminants to build up on rooftops.

Heavy metals have also been detected in rainwater collected from rooftops.

Depending on how you intend to use your rainwater, this may or may not be a concern.

You may install a “first-flush” diverter.

  • First flush diverters
    • First-flush devices (also known as roof washers) are effective because they remove contaminants before they enter the barrel.
    • The first several gallons that run off of a roof, gutter, or other surface are the most likely to contain contaminants.
    • A first-flush diverter will prevent these first few gallons from entering the storage barrel.

Is algae a concern in rainwater harvesting?

  • Algae growth can become a problem in barrels that are translucent or lighter in color.
  • Wash it out with a very dilute (2%) bleach solution; rinse your barrel very well after washing.
  • Be very cautious of watering edible plants with water from an algae-contaminated barrel as some algae produce toxins that are harmful to humans.

What if my rain barrel overflows?

Overflow of rainwater can potentially damage your home’s foundation if the barrel is up against the house, or the water isn’t going where you want it.

  • Your barrel must have a hole for overflow about 2-3 inches from the top of the barrel to allow sediment to settle.
  • Attach an adapter to this hole for a hose.
  • Direct your overflow hose to your landscape so that you can make use of overflow rainwater as well!
  • You can also use overflow holes to connect two barrels together.