by Wendy Diaz
The recent international health alert of the Zika virus1, which is transmitted by infected mosquitoes, has me pondering all the rain barrels in Durham County that were installed after the 2007 drought and whether or not they are sufficiently maintained to avoid them becoming breeding vessels for mosquitoes. According to the best surveillance estimate by The Centers for Disease Control and Prevention (CDC), North Carolina is within the potential range2 of the Aedes aegypti mosquito; the species of mosquito most likely to spread viruses like Zika. The CDC cautions that the maps they provide “do not necessarily mean that there are infected mosquitoes in the area” so don’t panic yet. According to the CDC, no local mosquito-borne Zika virus case has been reported in mainland United States but there have been travel-associated cases. I am using this news item to remind gardeners and homeowners that their rain barrel requires some light maintenance so they continue to operate optimally as a useful supplemental storage for our watering needs and to prevent them from becoming a health and safety hazard!
Mosquitoes need standing water to complete their life cycle3. Most species of mosquitoes require at least 10 to 14 days to complete the aquatic stage of their life cycle (egg-larva-pupa). Modifying or eliminating breeding sites is the only long-term solution to severe mosquito problems3. To prevent adult female mosquitoes from laying eggs in your rain barrel some routine maintenance3,4 is recommended.
- Drain your rain barrels regularly.
- Clean gutters of debris as needed and at least seasonally so they drain well and don’t accumulate water.
- Wash and flush gutters annually5
- Check mosquito screens periodically to make sure they are secure without gaps and are not blocked by debris. Replace the screens if they have any holes.
- Seasonally drain sediment-laden water through the bottom valve especially after pollen season.
- Check gutter connections after intense rainfall or storms for damage and check gutter connections every 3 to 4 months for damage.
It is not recommended that bleach be added to your rain barrel because it can be damaging to other aquatic life if you use your rainwater for multiple purposes other than watering plants (e.g. fish pond or bird bath) and there are less harmful methods available that are more environmentally friendly6. If you check your rain barrel and see larvae or “wrigglers” you can do one of the following7:
- Pour a few teaspoons of vegetable oil in the water. This will suffocate mosquito larvae on the surface of the water.
- Put mosquito dunks in the rain barrel water. This solid commercial formulation is a larvaecide and contains the bacteria (Bti, Bacillus thuringiensis israelensis) and it kills feeding mosquito larvae and does not harm humans, animals or plants.
- Label your rain barrel to remind others that the water is for non-potable/outdoor water use only and Do Not Drink!4
- Rinse thoroughly if you bleach your barrel to remove algae. I use a dilute solution of laundry solution after pollen season in late April.
Most rain barrels purchased commercially and those adapted from other uses do not have a overflow or outflow in sufficient diameter to release water when the barrel reaches its capacity resulting in overflows during a major storm. A ‘waterfall effect’ can cause erosion of the soil beneath the rain barrel. And for this reason, make sure the overflow is aimed away from the foundation of your house.7 To avoid this, the rain barrel overflow must be able to handle the same flow as the gutter system feeding into the rain barrel4
No doubt, over the years you have learned the limitations of your rain barrel collection system or it is old and is not performing optimally and realize it is time for some upgrades to decrease maintenance and increase sustainability. A leaf eater or some sort of filter will help divert debris and leaves from your rain barrel. A first flush diverter reduces the level of pollutants and debris in your rain barrel. A first flush water diverter diverts the first few gallons of rainfall (the most polluted) from your gutter and away from your rain barrel9.
- If you have a light-colored barrel consider painting it a dark color or covering it with wood-like wrap to prevent sunlight penetration and algae growth.
- If you use corrugated piping to connect overflow to your rain garden use a smooth sided flexible piping so that water does not accumulated in the creases and provide habitat for breeding mosquitoes.
- Install a first flush diverter or a leaf eater to block debris.
Does your rain barrel set-up have the components shown in the figure below8? If not, consider some upgrades and don’t forget your basic maintenance. Harvest rainwater without your rain barrel becoming a mosquito nursery!
- Herald-Sun, The (Durham, NC); February 24, 2016. Keith Upchurch Spring to bring Zika-carrying mosquitoes.
- https://www.asla.org/uploadedFiles/CMS/Meetings_and_Events/ 2011_Annual_Meeting_Handouts/MONB10_From_Catchment_to_Reuse_Designing%20and%20Implementing%20RAinwater%20Harvesting%20Systems.pdf