Safe Rainwater Harvesting Catchments

Any catchment area will pick up some contamination from leaves, bird droppings, dust, and other natural causes. This water is fine for watering your garden, but it will need a good filtering system before you can be sure it is safe to drink. Some roofs, such as old tar and gravel or old asbestos shingle roofs create too much contamination for rainwater harvesting. Treated cedar shakes are also not recommended for water harvesting.

The type of gutter system you have is also important, as many may have lead soldering or lead-based paints. Additionally, if you live in an area that produces heavy industrial pollution, your rainwater itself may contain some undesirable contaminants. Talk to your local municipal government about the issue of environmental contaminants in your area that may affect rainwater quality.

{ 15 comments… read them below or add one }

Paul April 24, 2010 at 2:28 am

How do you keep Mosquito’s from breeding in the rain barrel?


steve May 6, 2010 at 3:32 pm


There are several options. First you could buy some screen and cover the whole where the water enters the barrel. The same screen you use for a screen door or window will work and can be found at your local hardware store.

You can also buy a product called Mosquito dunks or Non Toxic Mosquito Control Bits. They kill the larva but will not harm the water.

I have link to them below:


Chenique April 24, 2012 at 2:28 pm

Hi Steve, GREAT website. Just wanted to comment that there is research showing that the dunks will also kill fireflies. The dunks use the bacteria Bacillus thuringensis to kill larvae, and these bacteria attack fireflies as well.


J.Burgen April 25, 2010 at 5:03 pm

I need an answer on possible problem of water in barrel becoming badly odorous. Our system, even with a screen, still ends up with small debris getting through due to our heavy tree cover. Someone told me that smelly water was no problem to water plants; but right now due to good rains I have a full pretty smelly barrel. Any suggestions?


steve May 19, 2010 at 4:14 pm


Stagnant water can be smelly; however not knowing what the barrels may have been used for before you used them as rain barrels puts me at a disadvantage. Try emptying them and using vinegar to clean them out. Then make sure they are a dark color and kept in the shade to help reduce the amount of algae growing inside.


linda May 8, 2010 at 7:34 pm

If you do not plan on using the water for drinking THE BEST way is to put a couple of cheap feeder goldfish in each barrel! I use several open barrels and they do a good job of eating the larve! They work for free and are always on the job! They are better than screens as those DAMN bugs always find a way in. I can’t imagine why anyone would want to use anything else. If the fish can live in the water you know it is fit to give to your plants!


Sheila April 26, 2012 at 7:46 pm

Mosquito Alternative;
rather than using the mosquito dunks, try this!
In large/full size spray bottle, combine 1 cup vegetable oil & water (yes, rain water works fine). Spray the surface – the oily sheen lets you know it’s in place. The oil prevents larve from breathing, thus killing them.


Joy May 2, 2012 at 7:51 pm

We have a rain water collection system from a cedar shingle roof to water our plants with. It it safe to use this water to water vegetable plants that will be injested? The roof was treated with some sort of tint about 5 years ago, Thank you.


steve May 4, 2012 at 3:19 pm

@Joy, Yes, the water from your roof, even after being treated 5 years ago is safe to use to water your garden and other plants.


Cornelia May 31, 2012 at 12:16 am

When winter arrives, do I drain them? Or do I allow the water to freeze?


steve June 1, 2012 at 2:33 pm

@Cornelia, To winterize your rain barrel its best to drain the barrel completely and leave the valve open. If you live in an area with hard freezes you should consider disconnecting it completely so no water is allowed in.


David September 1, 2012 at 8:12 pm

How long will rain water last? Should it be used right away?


steve September 4, 2012 at 7:35 pm

@David, Typically you have a week or two before your rain barrel begins to grow algae. However you can add a teaspoon of bleach per 10 gallons of water to delay the growth of algae or mold in the rain barrel.


Steve December 13, 2012 at 12:54 am

I would like to run a hose from a rain barrel spout to fill a trough for watering chickens. The water would come from a gutter downsput from a new shingled roof. Do I need to add any anything to the collected water to make it safe for the chickens? Thanks!


steve December 21, 2012 at 3:22 pm

@Steve, What type of shingles? If composite you may want to consider using another source of water. If wood then it should be fine.


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