Rainwater Harvesting in WNC

                                                              Pie chart of residential water consumption

In cost-effective water conservation, we explore techniques for the quickest environmental and financial paybacks. We use a similar mentality to assess rainwater harvesting in our local Asheville and WNC region.

If one gardens or irrigates thier landscape, outdoor water use is where to focus. Over 50% of an average US home's water is used outdoors. Reducing water usage outdoors has the biggest impact on how much water a home uses. 

Word of Warning

Bulk rainwater storage right next to a foundation can introduce considerable risks of durability and failure. Basements, crawlspaces and improperly sloped finish grade increase concern. Be sure finish grading improvements are done prior to re-routing gutter water. Maintenance is imperative to ensure that filters are clean and overflows are operating to reduce any negative impacts of bulk water, #1 on our top 3 ways water destroys homes and buildings.

Rainwater Harvesting for Outdoor Use

Rainwater harvesting makes the most sense for gardeners or those that irrigate the landscape. For those with well water, pumping water from underground represents a big use of electricity and hard (alkaline) water risks upsetting soil PH levels. For high performance homes, it's possible the well pump will be one of the biggest energy users in the home.

Rainwater systems have upfront costs and extra maintenance. The more water used outdoors, the deeper the well, and the more expensive the city water, the more it makes sense to include rainwater harvesting systems.

If not on a septic system, city or municipal water providers usually charge sewer fees based on how much water is used. Outdoor water users can save significant sewer fees by using rainwater systems instead of city water. Depending on usage amounts, having a dedicated agriculture meter installed is usually more cost-effective than rainwater catchment if treatment chemicals are not a concern.

Gardens, Landscaping and Soil, Probably Prefer Rainwater to Chlorinated

Water from the treatment plant has chemicals that could be harmful to soil organisms. Flouride, Chlorine and chloramine are widely used in city water sources. Aquariums or ponds should avoid water with chlorine or chloramines. Most researchers seem to be fine with chlorinated or chloriminated water with some exceptions. Compost tea, bonsai and other container garden enthusiasts typically prefer water without these suspect chemicals.

Rainwater Catchment for Indoor Use

For most projects in the Asheville and WNC region, rainwater catchment is hard to make cost-effective for indoor use, mainly because there is usually easier access to a well or city water. With that infrastrucure in place, justifying extra expense is tough given the average depths of wells and cost of city water.

For heavy outdoor water users, a nice upgrade is a rainwater system plumbed for the hose bibbs only. This involves plumbing and pumping the rainwater inside to supply the hose bibbs which use the water outside.

Supplying toilets and washing machines are next steps  while potable water represents the highest costs and complexity. A few rare projects dont have any other options and hopefully these types of systems will continue to become more affordable and efficient. Roof material becomes an important consideration in potable applications and the safest materials tends to be very expensive.

Rainwater Catchment on the Cheap

Most rainwater systems in our region are for gardens and landscapes. They tend to have a DIY nature although Higher Ground is a regional contractor offering professionally installed systems of all types. 

Remember the bigger picture. Proximity and extra risks to the foundation is an important concern. Very expensive trouble can result compared to smaller returns of rainwater catchment if executed poorly. The safest systems are well designed, highly maintained or plumbed to a storage location well away from the foundation.

Gravity Vs Pump

Gravity tends to simplify but many situations demand pumps. We recommend exploring gravity options first.

Tall tanks are the main answer to simplifying with gravity. Their extra height helps increase pressure from the tank or outlet. Tall tanks tend to be expensive and hard to hide. Choices for style and materials are limitless and the best designs are integrated into the architecture. 

The best sites for more affordable, safer and hidden rainwater systems, are those with gardens or landscapes, downhill from the home and roof. Walk-out basement lots with plantings at the walkout level fit this description well.

50 gallon drums are a common solution but offer miniscule storage capacity. We have success with locally stocked 275 gallon containers. At $120, and 44 cents per gallon, they are a good value compared to rain barrels and smaller, commercial rainwater cisterns. Most of the expense and complexity is in plumbing the gutter to the tank, using screens or diverters and providing an overflow path.Picture of rainwater system at West Asheville Springtime Cottage.

This simple system is on the West Asheville Springtime Cottage. The lot begged for it, with a high spot 12' away from the gutter. A first flush diverter is accessible at the corner.

Uphill is safe here because leaks, clogs or overflows are directed around the house in a swale (ditch).

Downhill is safer but the higher the tank, the better chances of using gravity without a pump system. 

Here are the author's two systems. I capture around 90% of my home's roof area to water bonsai attempts, make compost tea and water extensive plantings. The filter system keeps the tanks clean enough to allow direct drip irrigation, with only one additional filter for the drip emiters. 

Rainwater system picture Rainwater system first flush diverter and geolid can filter. Top view of rainwater system picture. Picture of rainwater can overflow.
275+ gallon rainwater system. These common tanks come in white plastic. A double layer of geotextile offers a durable sunblock for algae. We get our containers from M and M drum in Canton. Water from the gutters fills a first flush diverter, then spills into the trashcan which has geotextile fabric for a lid-screen.  Top view of the filters and overflow. Fernco parts offer flexible, and serviceable connections. Inside trash can with fabric removed. Concrete epoxy attaches the end of the 4" PVC, to the inside of the can and seals the penetration on the way to the tank. Slots are cut in the PVC.
Picture of large diameter plumbing for hose bibb. Picture of rainwater system. Top view of rainwater system.
This setup is a gamechanger for strong water pressures from barely elevated storage tanks. For more gravity pressure, stick with bigger pipe diameters and pay attention to any fittings that restrict flows. This gate valve part coming off the 1" PVC, allows full flow and 3/4" hose thread connections.  This 325 (275+50) gallon system occupies my carport corner. The first flush diverter is on the left. A pretty easy system uses 4" to 2" reducers to allow use of the common 2" gate valves. Bulkhead unions are used to add smaller outlets to trash cans and 50 gallon drums. Top view shows a plumbing arrangement that sends the overflow back the same direction it came in. Rinsing the geotextile is required every couple rains.

Picture of rainwater pillow under deck.

Many dont have room for a tank so options like this rainwater pillow can make sense. These can fit in tight quarters like crawlspaces and under decks. They can be quite durable. Think white water raft.

Rainwater illustration cut away view

Rainwater system illustration


Underground storage is the most desireable solution for most. These setups tend to make the most sense with new construction or renovations involving earthwork. Septic tanks are a good fit for this purpose. 

Picture of foundation dedicated to rainwater storage.

In locations with no well water or city water, large underground storage capacity is often integrated into the foundation design. This is a common solution in the Caribbean and increasingly being used in western states with high water costs.



While most rainwater catchment projects in our region are small, they can have a big impact on overall water usage. Water continues to become more scarce and expensive, even in our region of plenty. We think those that irrigate thier landscape or use a lot of water in their gardens are a good fit for including rainwater catchment systems.

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Springtime Builders is an Asheville NC custom green builder specializing in cost-effective energy efficiency and building science best practice.


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