I've been religiously using rain water for my houseplants, but read somewhere recently that if your tap water is safe to drink, it's safe to water your plants with. Wondering if I have fallen for an urban myth with the rain water thing:)

I use tap water for my plants, no choice here, we have 6 months of no rain. But if you do have access to rain water that is really good!

Though tap water varies from place to place, it is also the frequency of watering and the type of media you have for whatever type of plant you are growing that will affect the watering needs of your plant.

Just adding, only exception from tap water use are for my carnivorous plants. If rainwater is not available, I use distilled water for them.

Thanks Tarev:) We live in pretty dry climate too, but we have rainwater for most of the year in our tanks. Our tap water is notoriously hard so I suppose it can't hurt to stay on the safe side and use rainwater.

Hard water has excess mineral salts that tend to build up over time and damage plant roots. So it is best to use filtered, distilled or rainwater.

WillC said:Hard water has excess mineral salts that tend to build up over time and damage plant roots. So it is best to use filtered, distilled or rainwater.

Does flushing the soil remove those?

I use tapwater as I don't have access to rainwater (I live in an upstairs apartment). The compost does occasionally have salts build up but I get rid of these when I repot. I've had plants for many years without them suffering.

I used to water my plants (very long ago) with hard, chlorinated, water. No problem. It all depends on what you are growing. Plants like the above mentioned carnivorous plant from peat bogs usually hate minerals and will die on average tap water. They hate the minerals just as bad as plants growing on mineral rocks hate the acidity of peat. So check your tap water (your supplier has it probably on its website) for mineral level, and check your plants for their favourite water. If your tap water is to hard, dilute it or replace it with rain water or bottled low mineral water. If your water is very low on minerals and your plant prefers high: add some powdered calciumcarbonate (chalk) every half year to the pot.
Fortunately, most common houseplants do not care.

Ruud

Thanks everyone, lots of great info:)

I used tap water for decades, then started catching rain water. HUGE difference! Not all tap water is the same but my plants look soooo much more happy with the rain water. If I had not seen the difference, I would have never known how much more happy my plants could be, how much better they could look. I do use some tap water over winter out of convenience, but still try to collect some rain for Dracaenas & Bromeliads with cups during that time, & for any others for which the difference seems to be the most dramatic.

The condensate from a dehumidifier or drips from an A/C would also be water to which nothing is added (aside from maybe some dust.)

Hamwild - Yes, flushing the soil with clear (mineral-free) water will wash out the excess mineral salts.

WillC said:Hamwild - Yes, flushing the soil with clear (mineral-free) water will wash out the excess mineral salts.

purpleinopp said:I used tap water for decades, then started catching rain water. HUGE difference! Not all tap water is the same but my plants look soooo much more happy with the rain water. If I had not seen the difference, I would have never known how much more happy my plants could be, how much better they could look. I do use some tap water over winter out of convenience, but still try to collect some rain for Dracaenas & Bromeliads with cups during that time, & for any others for which the difference seems to be the most dramatic.

The condensate from a dehumidifier or drips from an A/C would also be water to which nothing is added (aside from maybe some dust.)

This is a silly quesrion, but how do you store rain water and for how long? Does it start to smell or grow?

Not silly at all. I catch the rain in buckets & then store any excess in laundry soap & milk jugs with the lids on, and to make sure the buckets get emptied within 5 days so I don't start a mosquito farm. It does not change in any way, that I can see or smell, except when it all froze this past winter. If there are a lot of leaves, it can start to look like tea but I don't store that water, just use it somewhere right away :+)

purpleinopp said:Not silly at all. I catch the rain in buckets & then store any excess in laundry soap & milk jugs with the lids on, and to make sure the buckets get emptied within 5 days so I don't start a mosquito farm. It does not change in any way, that I can see or smell, except when it all froze this past winter. If there are a lot of leaves, it can start to look like tea but I don't store that water, just use it somewhere right away :+)

I store mine in a ~70litre PVC reservoir. It does not go smelly or stale or whatever, though it indeed may discolour at times. In dry periods, when I see the bottom of the reservoir, I clean it from organic debris.

The above mentioned Bromelia do usually grow good on rain water with added fertilizer. As epiphytes they are used to a low mineral diet. But not as low as pure rain water! The water flushing down a tropical forest picks up lots of minerals from the trees themselves, bird-droppings, rotting leaves etc. This was revealed in a study by the Michigan State University (MSU). They studied the tropical rainwater as washing down the plants (and not as it falls!). Fertilizers based on their findings are often known as MSU fertilizers. Among orchid lovers here in the Netherlands and Belgium all users of it are very enthusiastic about the results on our plants.

Small warning on rain water: take care if you live in an area with lots of air pollution. The rain water may be too acidic (but don't worry in any 'normal' region). In times passed we once measured rain water with pH=2 (instead of ~5, rainwater is slightly acidic due to dissolved carbondioxide), that is 1.000 times more acid than it should have had.

Ruud

I'm a rainwater fan, though I fully trust Will's advice. I liked this article- granted, a lot of anecdotal evidence, but I trust Geoff too

Partly, I feel a tiny bit virtuous not using electricity pulling groundwater when not needed. Partly, plants very happy, and no worry about minerals in 'office' plants which aren't as convenient to flush.

I just tested my rainwater with paper strips, it looks about 6.0. Not terrible, I don't think. A quarter teaspoon baking soda in about a quart water raised it to about 8, so it doesn't take much to change that.

Buy a TDS (Total Dissolved Solids) meter, they cost about $15 or so on Amazon. The lower the reading the better the water.

I use rainwater mainly for my carnivorous plants and houseplants. My rainwater TDS reading is typically 2ppm. The veggie garden gets tap water from the hose.

It is interesting to hear everyone's experience on this question.

I use our incredibly hard tap water for all my potted plants (almost all succulents) except the baby seedlings and the plants in unglazed clay pots. Those get purified (reverse osmosis plus) drinking water.

I see no problem with hard water for any of my full-grown plants (the problem with the unglazed clay pots has to do with the salt buildup on the container after evaporation). I flush every container when I water. Maybe 1/4 the volume required to wet the soil passes through at the bottom. No special ultra-pure water is required to flush if you're regular about it. Alternatively, you can leave your house plant out in the rain every once in a while to let nature do the flushing slow and proper.

Our tap water varies widely in color and hardness from day to day (word to the wise). It's typically quite high in general hardness (GH) and carbonate hardness (KH), with a pH above 9. The main issue with hard water (if your tap water comes out of the ground like ours does) likely has more to do with its pH than its mineral content, if you flush in the manner I have described. The harder the water, the more dissolved carbonate, and the higher the pH. As a general rule. These things can all be measured with aquarium kits. Roots tend to function best at a pH at or slightly below neutral, where most nutrients are available. Around the pH of ordinary unpolluted rain water.

So I compensate for the hardness of the tap water I use for almost all my plants by acidifying it first. I use a product for planted aquaria (bisulfate) to adjust the pH to near 6. You can use various other things too. That's even more salt into the water, but salt of the right kind, and my plants definitely appreciate the extra effort.

It is my understanding that succulents can tolerate higher pH and levels of mineral salts than non-succulent tropical plants.

If you fill a jug and let it sit overnight, a lot of what they consider might be harmfull gets ... removed ... evaporated .... by morning; not sure of the right terminology. That's what I've always done, based on an article I read years ago. Seems to have been fine.