Hard Water vs Soft Water for Houseplants

Question

I have read that certain house plants should be watered with soft water. I would like to know if this applies to all house plants and what consequences would be visible when watering with hard water vs soft water.

I always use hard water just because it would be difficult to obtain soft water, even buying it since I live on a limited income and do not feel justified with an extra expense.

Most of my plants seem to be healthy and growing even with the hard water. Is the 'soft water' watering a recent suggestion? (recent as in the last 20 years of so?)

An example of a similar situation would be drinking bottled water vs tap water. It is a recent trend, there are articles that properly prepared tap water is better than bottle water, since bottle water filters out some trace minerals that the body needs, plus the plastic bottles are an environment issue and legal issue concerning water rights to lakes and streams. So the recent trend of bottled water vs tap water may be a contrived issue.

Is hard water vs soft water a similar situation? If not, what makes it not and why is it considered important?

Thank you for all the responses, all very informative and extremely helpful.

Answer 1

To some extent, it depends where you live in regard to using tapwater for your plants, because different countries may use different chemicals to ensure it is potable, though generally, tapwater isn't a problem for potted plants. Different areas or regions within a country may naturally have either soft or hard water though, and that can be important where ericaceous plants are concerned; hard water means it may contain lime (calcium carbonate). Using tapwater in a hard water area to water pot plants means, over time, you will notice a yellowish white crusty rim on the inside of the pot, and sometimes, as the soil dries out, perhaps a small amount of the same deposit dotted about on the top of the soil. This causes no harm to the plant in the pot, unless it's one that particularly dislikes lime (ericaceous plant).

A lot of warnings are often given about a 'build up salts' in the soil in the pot; this refers to what might be left behind by frequent fertilizer use. If you do not use fertilizer for your plants all the time, or only use it at minor to moderate levels, this won't be an issue either.

I live in the UK in a hard water area, and other than for any ericaceous pot plant, I have always used tap water with no problems apart from the scale build up on the inside of the rim of the pot after a couple of years. For ericaceous (acid loving/lime hating) plants, either clean rainwater or previously boiled and cooled water is better, because boiling takes out the lime (and leaves it all over the inside of my kettle...) Further advice on watering plants here https://www.rhs.org.uk/advice/profile?PID=691

Answer 2

If ever possible it is best to use distilled or RO water. This is not always possible. The risk is possible build up of the mineral salts in the soil in the pot. This and fertiliser gives that white crust around the top of the pot. What we all should do it flush out our plants every 4-6 months. This requires pouring the 4 times amount of water to soil in the pot. If the pot hold 1 litres (1 quart) of soil. Pour 4 litres (1 gallon) of water through the pot. Best to do twice, but once will do it. If you water from the top you are less likely to get as much salt build up. But, if you water from the bottom some salts are not washed out at each watering. People that bottom feed should do it every 3 months.

University of Maryland Watering and Soluble Salts

SF Flush Plants

Answer 3

Unless you're gardening in a production greenhouse or hydroponically, it's fine to use hard water/tap water. As noted in the Univ of Maryland article in GardenGems link, it's best to let municipal water sit overnight to ensure that the chlorine is cleared from it.

Like @Bamboo, I've used hard water for decades with no issues (I don't have any ericaceous plants, however). The only time I've gotten the crust Bamboo mentions is when I used fairly hard well-water.

IMO, you should never use water softened by a water softener for watering plants (especially indoor plants) because the softening process can cause sodium buildup in the soil.

Here's an interesting article from a company that makes and sells water softeners.

Answer 4

Most plants in good healthy soil can handle hard water as the soil provides the nutrients and regulates PH naturally.

But if you use industrial growing methods (e.g. hydroponics) and you need to add fertilizers to the water then it becomes important due to PPM

Parts per million (PPM) is how much stuff other then water is in the water

If you start with london hard water at 300 PPM, and then add fertilizers to that water, you may raise the PPM level as well as change the PH of the water. You may easly end up with well over 1500 PPM which is too high for most to be able to absorb nutrients known as (Nutrient lock out).

Nutrition lock out: This is bad for the plant; at the atomic level the plant will simply be unable to absorb the nutrients as there are too many particles in the water knocking out the ones trying to "lock in " to the roots.

Also some hard water leaves a residue in the plant's "plumbing" leading to blockages and affecting overall growth but not so obviously.

Don't forget roots need to breath, if they are coated in residue left by hard water, they may have less surface area to absorb oxygen via the roots, decreasing their efficiency.

Answer 5

When it comes to watering plants it's all about the PH of the water or growing medium.

If you have "hard water" it is likely that the PH would be A bit off but most good healthy living soils would "buffer" the PH and correct it.

The biggest issue is if the water used contains chloramine and chlorine as disinfectants

Hard water would contain minerals found naturally in the water and added chlorine and chloramine

The last 2 raise the PH and PPM of the water and they KILL advantageous bacteria and fungi that help the roots grow better (also found in our gut and AKA second brain! Google it bro).

As above so below! The plant would be much happier with a good root system!

To get rid of chlorine simply allow the water to sit in a bucket or bottle with the lid open and it will simply evaporate all the chlorine with in 24 hours If you are in a rush use an air stone and pump air in to the water like a fish tank that'll do the job in 4 hours. You will notice that the PH level has dropped up to 1 point as the chlorine has gone from the water. The chloramine is different, it does not evaporate!

Some people use more chemicals in aquariums to "breakdown" the chloramines to amonia...I would not advise you do that if you plan to eat the plants you are taking care of.

To test you water quality you will need PH tester TDS meter Tap water That's it :)

My tap water is at 300 PPM PH8 straight from the tap PH7 after 24 hours removing chlorine passively.

So I need to use bottled water from the supermarket at PH6.2 and 70 PPM.

Conclusion

Its important if you are adding nutrients to "hard water" keep track of your PH and PPM as it may send those out of wack and kill the advantageous biomass that we call soil.

If you use tap water then use good soil simply remove the chlorine to help save the beneficial living soil. You will find that microbes have a remarkable ability to regulate the PH to something more comfortable for them and the plants.

Answer 6

Naturally speaking, in most common cases plants receive their water from rain which is 6.2PH and should have very low PPM counts.

Tap water that is high in impurities is referred to as hard water.

I have hard water here in London at 300PPM and 8PH The water mainly contains lime, It also contains chlorine and chloramine

After letting the chlorine evaporate overnight I get 7.2ishPH but still 300PPM

8PH is too high for most plants 7.2PH is also too high for plants Plants need 5.5-6.5PH to be able to absorb and use the nutrients correctly.

But thankfully if you have decent living soil then the microbes will regulate the PH of the medium to around 6PH !

But the chlorine and chloramine kill the beneficial microbes in the soil and in our bodies! (Google "second brain in our gut")

If not dealt with, chlorine will slowly evaporate and effects the growth of the plant specifically the roots.

In humans it causes depression!

So for best results I currently have to use bottled water at 70 PPM and 6.2PH until I get a filter.