Before you buy a rain barrel or install rainwater catchment systems, consider feasibility. Is it worth it?

Is it just because you hate to see all that potentially useful water be wasted? Can you see a rainwater catchment system used to irrigate your landscape? The answer is usually yes. But the question then becomes, how much water do you need to irrigate your landscape on a daily, weekly, monthly basis?

Here are some steps to determine what kind of system you should design:

  1. Determine how many gallons of water your irrigation system needs to deliver to the landscaping

The average daily water use in the Sedona area is 360 gallons per day per person/household. Outdoor use is estimated at 30% of that, so let’s use 100 gallons per day for outdoor use, which we will allocate to landscaping.

Let’s say your landscape irrigation system is set up to water 10 trees, 100 shrubs, perhaps some pots, and a garden area. Using rough figures, that is about 700 gallons per week.

  1. Determine the catchment area based on the square footage of roof area for you house and determine how much volume could you potentially collect

Most homeowners who start out rainwater harvesting using a barrel or several soon realize they are actually losing out on capturing a large amount of water. A typical 55 gallon barrel can fill up in only one hour with a 1/8” of rain on 1000 square feet of roof area. That single rain barrel will hardly make a dent in your irrigation needs. Besides, your landscaping is being irrigated to an extent during the rainstorm and so you should look at the function of the rain barrel as a storage system to capture the water for later use during dry periods, not during the rainy periods.

A rainwater catchment system based on a couple of rain barrels may not seem to be worth it if your intention is to capture as much water as you can, store it and use it for your landscape irrigation needs.

 

 

 

 

 

  1. Determine the feasibility of having a single large collection tank or if several tanks would be needed because of the way the roof gutters and downspouts would have to be designed around the house and the site conditions.

The question of feasibility is both a factor of your site suitability and economics. Here are some site suitability factors:

  • Adequate roof catchment (sufficient area and fitted with gutters and downspouts)
  • Suitability of area at base of downspouts to accommodate the plumbing necessary to channel the water into barrels or a storage device
  • Number of suitable downspouts relative to required storage volume
  • Aesthetics of plumbing, tanks and trenching needs
  1. Determine cost to install the system and perform a cost-benefit analysis.

You may compare the cost of a rainwater catchment system vs. the cost savings of paying for the water and realize that water is so cheap that you will never break even. Capturing rainwater for your own use to offset the cost of paying for municipal water is not the point. Rather, it’s the green lifestyle and ecological stewardship values that drive your decisions. But it still comes down to how much is that worth? How high tech should you go with capturing rainwater?

  1. Based on cost-benefit analysis determine if you will design a low tech, limited collection system or a high tech, high volume system. This decision will be based on the costs involved for each system and how much you are willing to pay.

It may be that to provide close to 100% of your landscape irrigation needs, you would need a 5000 gallon tank or several smaller depending on the design of your roof catchment area and the ground level suitability to bury and or hide the tanks.

The cost of implementing a system that is designed to pump water out to a garden, an accessory garden hose or other high pressure use can significantly add to the cost of an otherwise passive gravity flow system. Most serious rainwater storage systems pump the water to where it is designed to be used, otherwise, you must rely on gravity flow alone and the use must therefore be downhill from the output elevation of the storage tanks.

In addition to overall cost, your particular site will dictate what kind of system is feasible. You may not have the room nor be willing to spend the added cost to bury a large tank. Remember, if your landscape irrigation needs are 700 gallons per week, you will need a lot of storage volume otherwise you will run out of water quickly. If that happens, why have a water catchment system that cannot store the maximum amount of volume to provide for your needs? It may be that is all your site can handle as well as your pocketbook.

Conclusion: After going through the process of design and feasibility analysis, you may decide that it is logical to consider reducing the amount of water that you need to capture to irrigate your landscape. Splitting up the amount of water you capture between a pressurized system for irrigation valves vs. a gravity flow system may be a good decision.

The gravity flow system can serve to irrigate native plantings and otherwise keep water on site and not runoff the property into the stormwater drainage system. Shallow retention basins can be created as well as large wells surrounding trees. There must be adequate pressure created between the points of discharge at the storage tank and the downhill elevation at the end of the hose.

Given the potential complexity of retrofitting a rainwater catchment system into an existing landscape, it would be ideal to design the landscape based on using rainwater catchment so the entire system is efficient and cost effective. Otherwise you may decide that a rainwater catchment system after the fact is not worth it.

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