Which Water is Better for the Garden?

When you become a gardener, the idea that water is a precious yet essential resource reaches a whole new level. Obviously, plants don’t survive without it, but water quantity isn’t the only consideration. Water quality, too, can impact your plants in a variety of ways, which is especially important when it comes to growing fruits and vegetables. This means that not only can water quality affect the size and abundance of your harvest, but your health as well.

No matter where in the world you live, water supply & quality isn’t guaranteed from year to year either (or even season to season). With the increasingly unstable weather patterns and severe weather events experienced over the past several years, we find ourselves making all sorts of adjustments and modifications to our water sources and watering regimes.

In practice, that might mean we use a mixture of tank, rain, bore, grey and tap water. But it’s worth asking the question, is any one of those sources better than the others? And is that always the case, or the case in all regions of the world? Here we’ll take a closer look at these and more, water-related questions.

watering sprayers in vegetable patch

Is Tap Water Good for the Veggie Garden?

Generally, tap water in countries like Australia, Canada, the UK & USA is fine to use on the vegetable garden, as it is treated with additives to ensure it is safe to ingest. You shouldn’t usually have any issues with regular tap water, but it’s good to be aware that it contains a few additives that aren’t good if they build up. Compounds like chlorine and fluoride are fine in small amounts, but if present in excess, they can build up in plant leaves and cause them to burn. Sodium, which is included as a water softener, can accumulate in the soil, which can damage its structure and make it difficult for plants to absorb water.

Tap water may absorb small amounts of lead, too. This can happen if water sits in copper pipes with lead-based solder, or passes through brass tap fittings. While frequent testing ensures Australia’s water is safe and meets strict water quality guidelines, excessive use of tap water on sensitive plants such as indoor plants and fruit trees may have negative effects on their health and growth. This is not to say that tap water will kill your plants, but it’s not the most natural of sources…and let’s not forget that tap water costs money!

What about Rain Water?

Rain water, especially that which falls during a thunderstorm, has unique qualities that can give your plants a boost. It is pH-neutral, additive-free, and contains nitrogen, one of the most important nutrients that you will learn about when you start gardening. Nitrogen is essential to chlorophyll production, so is vital to all plants (lack of nitrogen will cause plants to yellow & eventually die). Rain water contains nitrogen in the form of nitrate, caused by lightning & electrification in the atmosphere. Air is composed of 78 percent nitrogen and 21 percent oxygen and these two elements become ionized and combine to form nitrate. This process is called nitrogen fixation. So while nitrogen can come from other sources such as fertiliser, rain water is unique in its ability to fertilise & water plants at the same time.

Harvesting and storing our water in tanks for later use in the garden is a sensible option that many thousands of Australians have implemented in the past thirty years. While there is a significant cost to set up a tank system, it does give some insurance against drought, reduces watering costs and provides a better quality water for your food garden.

These 4 water tanks harvest rainwater from a house roof

Is Bore Water Always Safe for Veggies?

Bore water, aka groundwater, is water that is pumped up from underground. This in turn comes from rain that has naturally soaked into the ground and is stored in the minute spaces between soil and rocks. In many countries bore water tends to be salty, so its testing before use is strongly recommended. In fact, some regions of Australia mandate that it be tested before use, as its quality is so variable. Bore water has the advantage of (usually) giving a free and unlimited supply of water, however, the average suburbanite with a few veggie beds won’t have access to it- it’s more likely to be a concern for those on acreage or farms.

The variable quality of bore water is often caused by previous land use. As water makes its way down through the soil to the water table, it can pick up any number of chemicals, salts, minerals or contaminants. Land may have had pastoral, agricultural, landfill or industrial uses, all of which could affect the composition, pH & salinity of the groundwater lying beneath it.

Can I Use Grey Water?

Household grey water is another potential water source for the home vegetable garden. Grey water is essentially used household water which is not too dirty. It includes water from showers, the kitchen sink, & the washing machines rinse cycle (it does not include water from toilets- that’s called black water). As you might imagine, grey water is essentially tap water with some soap & other organic elements in it, so is generally free from any hard chemicals which damage plants. Nevertheless, the quality of untreated grey water can vary dramatically depending on the wastes it contains, plus which detergents & cleaning products are used in the home. For this reason, grey water is generally best used on lawns, ornamentals and fruit trees rather than vegetables- i.e. anything where the greywater doesn’t come into direct contact with the edible part of the plant.

The use of grey water in the garden can be as simple or complicated as you like. There are impressive setups like that at Jerry Coleby-Williams’ property, where a retrofitted system allows the entirety of the households grey water to be treated then distributed out to the garden to grow food. At the opposite end of the spectrum, using grey water can be small-scale and low-cost. It can be as simple as diverting water into a bucket and carrying it out to the garden- hello extra exercise!. You can do this with your washing machine hose, your shower water, bath tub water, or even just the cold water as it gets hot.

Most experts will advise using special aqua filters to get grey water as clean as possible for garden use, because it prevent soaps & chemicals from changing the soils chemical composition and pH too much. While this sounds ideal, in reality it might not be practical for the average backyard gardener. The best thing you can do when contemplating using your grey water on the garden, is to make sure you are using natural cleaning products that are low on harsh chemicals- here is a detailed run-down.


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