Are you watering with tap water?
City water contains chlorine and chlorine kills microbes – both good and bad. Will watering plants with tap water kill the beneficial microbes delivered through compost use?
Chlorine, chloramine, fluoride, and salts are used to treat city and household water systems. None of them are beneficial to plants, soils, or the microbial populations contained therein.
The good news is that if your city’s water system maintains chlorine at recommended levels, most plants won’t be harmed and soil/compost microbes will quickly recover.
Generally, chlorine also dissipates quickly. Fill a 5-gallon bucket with tap water and let it sit for a day or two before using the water on plants.
Chloramine, a compound that includes both chlorine and ammonia, is a little harder on plants and soils. It is used throughout the US, including a number of metropolitan areas served by McGill composting facilities. Check out this list to see if your water system is among them.
Over time, chloramine use can acidify soil and damage plants. If this chemical is running through your watering tap, keep an eye on soil pH.
Fluoride is added to drinking water supplies to strengthen teeth. It is also found in some fertilizers and perlite. Burned tips and edges of leaves can be a sign of fluoride toxicity.
Using compost to maintain a neutral pH will limit fluoride availability, as will switching to rainwater or filtered water.
Household systems designed to soften water using salts can damage soil and plants, too.
Short of installing a new spigot in the H2O line before it reaches the water softener, adding calcium to the soil through applications of gypsum or lime can help. So does simple leaching (over-saturating the soil to flush out excess salts).
But know that leaching will also wash away nutrients. If you opt for this method, be sure to add some compost post-watering to help rebuild the soil.
Collecting rainwater and mixing it with tap water can dilute the harmful impacts of chemicals and salts.
For home use, rainwater harvesting systems can be as simple as a $5 bucket sitting in the yard or as sophisticated as a $2500 tank set-up.
Just make sure water in open-top collection containers is not allowed to stagnate and become a breeding ground for mosquitoes.
Want more information about using tap water for watering plants? We found this article that discusses the various chemicals used in water treatment and how they impact plants and compost.