Is Tap Water Bad for my Plants?

Is keeping plants really as simple as we’re led to believe? Unfortunately not. We’re always told that plants plus water equals success, but as I have learnt during my time in this industry, the truth is a lot more convoluted. Imagine my frustration when I came home with my first carnivorous plant, only to watch it wither because I used water from the tap… the tap, that is quite literally the only source of water in my home. So that brings us on to this post: Is tap water safe for my plants? If not, what else can I use?

I think it's important to note, first of all, that if you are growing in the UK, 9/10 times, tap water is absolutely fine for you and your plants. At no point do we want to insinuate that the tap water here, which is generally well managed and properly treated, is unsafe for consumption, and that should be made clear throughout the following discourse.

What’s in our tap water?

Interestingly, water itself is not much of a beneficial compound to humans, it is the huge array of minerals that water is able to hold and transport which is of most importance to us. Resultantly, tap water in the UK includes a number of minerals in order to ensure its nutritiousness and has trace amounts of various chemicals that ensure its cleanliness for consumption. This means that UK tap water is both healthy and safe for consumption, which is a very fortunate position for us to be in.

UK tap water contains trace amounts of Chlorine that are determined to be safe by the UK water standards commission. This chlorine helps to rid the water of any possible bacteria or infectious disease that may lie present in the water before processing. Equally, fluorine is added among various other microscopic traces of cleaning chemicals, none of which are determined to be at an unsafe level.

Further, tap water in the UK famously contains calcium carbonate or ‘Limescale’, which is a harmless compound that contributes to the hardness or softness of water. This is a natural response to various elements forming compounds when water is heated. 

How does this affect my plants?

Most of the time, it doesn’t. A lot of discourse can be found online detailing the benefits of growing plants with filtered water, which is certainly true for some plants, but if you ask any keen collector or grower in the UK, you will find that most use tap water exclusively for no problem. In reality, chemicals like fluorine and chlorine are totally unnatural to plants, and they have no evolutionary equipment to deal with these chemicals, however: these chemicals are present in such small amounts that they are unlikely to be picked up in large quantities by plants, and the cleaning effect they have is likely to be beneficial to the alternative, as nasty bacteria and infectious diseases in untreated water could be much more harmful to them. 

The biggest debate is around the effects of hard water, and calcium carbonate. Calcium carbonate can be absorbed through the roots and build up inside the plant. For most plants, they are efficiently able to filter out these kinds of inclusions before they even enter the vascular system. Equally, a lot of soil mediums trap mineral inclusions and act as soft ‘water filters’ meaning the plant takes up water with significantly less limescale than that which was initially poured in. In areas with harder water, these issues are likely to be heightened.

What alternatives are there?

If you are still uncomfortable with giving tap water to your plants, then there are a number of easy alternatives to put your mind at ease.

Filtered water - Water filters, like Brita filters or similar products, help to remove various chemicals and minerals from your water: in theory making it safer to drink and resultantly, better for your plants. There is no harm to filtering water before using it on plants, and if it is something you have the equipment and time to do, it is certainly recommended. However, it is not something I would suggest to be paramount and instruct you to run out and get a water filter immediately! The results may or may not be noticeable, and the research as to how necessary it is is so far inconclusive. You can also find natural water filters, which are sticks of  activated carbon, which naturally absorb impurities from water by just sitting in it overnight, and can be used for up to a year.

Distilled water - Distilled water is not readily available in all places like tap water, but it can be procured online or from pharmacies and drugstores. Whether distilled water is good for plants or not is undecided. On the one hand, it certainly does not contain any of the troublin inclusions that may be found in tap water, on the other hand it equally does not include the beneficial nutrients and minerals that plants receive from tap water. 

Rain water - Rain water is certainly the best option for plants. However, it is crucial that rainwater is collected as it falls, not from stagnant sources like puddles. Rain water that has sat for a while can contain insect eggs, fungal spores, bacteria and infectious diseases. A water butt, or specifically designed buckets can collect and store falling water really well. Rain water also has a naturally lower PH value than tap water, and therefore helps to keep your soil acidity stable.

Plants for which tap water is unsuitable:

Calathea (Goeppertia) - Calathea famously have crispy leaf syndrome, where the contaminants in tap water gets deposited in the farthest extremities of the plant, leading to crispy brown leaf edges. Using rain water or filtered water is a certain way to combat this. Plants in the same family such as Maranta, Ctenanthe and Stromanthe, also fall victim to this but to a much lesser extent.

Bog plants (Sarracenia, Pinguicula, Dionaea, Nepenthes, Drosera etc.) - Carnivorous plants like these are adapted to live in environments with very little in the way of soil or water nutrition. This is why they eat flies - to account for the lack of nutrients they get from their root systems. Resultantly, they are unadapted to absorbing water with much in the way of minerals or nutrients at all. It is certainly wise to use distilled water or rainwater for these if possible, as tap water will likely kill them.

Alocasia - It is often claimed that Alocasia equally suffers from Crispy leaf syndrome, but this is debated, with a lot of Alocasia growers using tap water quite happily. If Alocasia is something you wish to start looking into and the quality of your tap water is something that worries you, using rain water or filtered water could help to put your mind at ease.

Others - Spathiphyllum, Chlorophytum and Dracaena are often cited on most online articles talking about plants with which to avoid tap water, but speaking from personal experience, I am yet to meet anyone who keeps this as philosophy. I personally have kept D. fragrans, D. reflexa, various Sansevieria, C. cosmoum, C. orchidastrum and S. wallisii and one of its more delicate, variegated forms alive happily and healthily without ever using any type of specific water, all of which remain alive and looking healthy to this day. This could well be due to my local water quality, and there should be no opposition to the notion of using filtered water to be safe. I can confidently say that, for these genera, filtered water is certainly not an absolute necessity as some online sources seem to suggest.