Tap water's chemicals like chlorine and limescale damage bonsai. A 900-liter rainwater tank and a £40 reverse-osmosis unit provide pure water that keeps foliage greener and eliminates mineral buildup, especially for lime-sensitive species like azalea and Acer palmatum.
Chapters
Tap water contains many chemicals that aren't great for bonsai— ammonia, chlorine, and chloride being amongst the worst offenders. In hard water areas, limescale causes many problems as well, particularly with the buildup of limescale on the trunk, on bonsai pots, as well as creating a white film over the leaves. Switching to rainwater and water obtained by reverse osmosis during the drier summer months isn't that difficult, and for a relatively small amount of money and effort, it's possible to have cleaner, more healthy water for your trees coming through your hose. The most important thing is to have some kind of container to store rainwater whenever it rains. The larger the container, the better. Simply because the water in it will last for longer. However, it's possible to have a clean water system with just a single water butt connected to your downpipe, collecting water from the roofs of your house or any outbuildings you may have. In my garden, I have anything up to 300 trees that require water at any one time. I've installed a large 900-liter water tank behind an outbuilding in my garden. And I use this to store water that falls onto its roof. If you shop around, it's possible to get water tanks of all shapes and sizes. I'm restricted as to how big a container I can physically carry through into the garden, so I have this narrow but wide water container as storage. Inside the water container is a Hose Lock Water Butt Pump, easily available from Amazon and other retailers. That will pump water the entire length of the garden with very good water pressure, even with a 30-meter length of hose. It's simply a case of plugging it into the power supply, dropping the pump into the container, and switching it on. The 900 liters will last me around a week to 10 days, even in the hottest of weathers. So what happens if I use up all of the rainwater in the container? That's where RO, or reverse osmosis, water comes in. A straightforward RO system is plugged into the mains water supply. Around half of the water overflows through a tiny pipe to the side of the container. The other half of the water is pure, very clean, that fills up my water container. The RO system cost me just £40 and so far lasted me A year or so between filter changes. The, uh, £20 filter sets remove all chemicals from the water and leave me with pure water. I keep it running 24/7 and it gives me 24 times 7 liter watering cans worth of pure water every 24 hours, enough to give my trees a really good soaking every day. This means I have no limescale or chemical problems for my trees at all. I am lucky, I also have 2 large, much cheaper 240-litre water butts that are connected near the top of the garden, and these tend to fill up faster, being fed by the house and 2 garage roofs. These water butts have a water butt pump that can be used to water my trees or have the water sent down to my main tank. That we've already seen. So is it worth the effort? Absolutely. My trees are greener, healthier, and they don't have a film of limescale built up on the leaves by late summer. And better still, the trunks of my trees and the pots are also free of limescale stains. Lime-hating trees such as azalea and Acer palmatum bonsai are also much healthier. The downside is that some bonsai like some calcium and a higher pH than rainwater can provide. These are now being given calcium via chicken grit and/or liquid silicon, dosed every month. Species that benefit from rainwater but then require additional calcium from time to time include many UK natives such as elm, hawthorn, blackthorn, and spindle. But overall, switching to rainwater, RO water, is definitely an improvement to the health and vigor of your entire bonsai collection.
