While some cultivators are lucky enough to enjoy a clean and reliable water source that’s readily available, that’s not the case across the country. According to NASA’s recent satellite data, 21 of the world’s 35 largest underground aquifers are losing more water than is being replenished, and reliably clean drinking water can no longer be taken for granted.

One of the worst mistakes a cultivator can make is to invest money into a garden, but neglect the issue of the water supply quality, perhaps the most important resource to having a genuinely healthy end-product.

Even if you believe your geographic area has “good” water, not investigating the water quality and irrigating your plants with contaminated water could choke their potential and undermine an otherwise perfectly engineered operation. If you wouldn’t drink the water at your house or cultivation facility, why would you give that same water to your high value crops?

Obtaining a water analysis to determine the source water quality helps cultivators decide if using a water treatment system would benefit their operation. Municipalities usually provide free water reports, however, it is up to the individual to test private water sources not supplied by the city. The EPA recommends testing household wells at least once per year, as the water in underground aquifers can fluctuate with the seasons.

Water Quality Basics

The overall water quality is usually based on the amount of total dissolved solids, or TDS, and is measured in parts per million (ppm) or mg/L. Dissolved solids are so small that they remain suspended in molecular, ionized, or micro-granular form and need to be removed at sub-micron levels using nanofiltration, distillation, or reverse osmosis.

However, the TDS is a generalized point of reference, as some contaminants can exist in even less than one part per million and can cause detrimental problems for your crops. For example, if boron is present in over 0.5 ppm, boron-intolerant plants may become stunted, with drastically decreased yields.

Another key indicator of water quality for plants is the total hardness, expressed as calcium and magnesium in grains per gallon (GPG) or ppm. With too much hardness, nutrient formulas can be thrown out of balance, and plant deficiencies or nutrient lockouts can quickly become a major problem.

Any water source with over 50 ppm of TDS of hardness should be purified. 50 ppm of hardness translates to three grains per gallon and is considered soft water, which few facilities have straight from the tap.

Getting Your Water Tested

The first step to getting your water tested would be to determine if your water source is supplied by the city, a well, or some other source like a pond, spring, river, or rain. Each type of water source presents a different challenge when it comes to choosing the right filtration method.

The type of water filtration system that is ultimately best for well water treatment may not be the same for municipal water users. While most well and spring sources require a sediment filter to remove sediment, city dwellers need carbon to remove chlorine and chloramines.


Cultivators using microorganisms such as beneficial bacteria, fungi, nematodes, mycorrhizae, and trichoderma must have chlorine and chloramine-free water for those beneficial microbes to survive and flourish.

All municipal water contains chlorine and/or chloramines as they are both powerful biocides, meaning they are designed to kill bacteria and sterilize water distribution lines.

Trace heavy metals like lead, copper, or iron from aging city water distribution pipes are becoming more common and even impacting human health like the lead present in Flint, Michigan’s municipal water. Additionally, hormones, pharmaceuticals, and all kinds of other toxic materials are increasingly making their way into the national water supply.


Water from well or spring sources are often high in minerals such as calcium, magnesium, sulfur, or iron. Giving water with too high of levels of these minerals to heavy-feeding plants will contribute to nutrient lockout and lead to deficiencies. Wells located in industrial agriculture sectors can become contaminated with high nitrates, pesticides, or herbicides used in modern farming practices.

How to Interpret a Water Quality Report

The following table shows the most common contaminants found in water, their sources, what harmful effects they can have on plants, and the concentrations that would start to affect plant health or facility operations. As one can see, many unknown dissolved minerals in an untreated source water can have the potential to damage high value crops.

Contaminant Water Source Potential Problems Ideal Levels
Total Dissolved Solids (TDS)Well, City Water with high TDS (total dissolved solids) has unknown contaminants that are the key cause of nutrient lockout and deficiencies in plants.< 200 ppm
ChlorineCity Biocide that kills beneficial bacteria, fungi, and microorganisms. Any healthy organic garden should be chlorine-free. Cultivators that use or brew compost teas or bioextract solutions should remove chlorine from their source water.0 ppm

Biocide that is a combination of chlorine and ammonia and is much more stable than

chlorine. It will not dissipate by bubbling or even by boiling off. It can only be removed by proper carbon filtration. It is toxic to beneficial bacteria, fungi, microorganisms, fish, and amphibians.

0 ppm
HardnessWell, City

Mineral hardness is made up from the calcium and magnesium dissolved in water and is the key cause of water problems in cultivation facilities. High levels of hardness in untreated water locks out key plant nutrients and forms calcium scale on equipment and tubing.

Calcium and magnesium are the most abundant minerals in tap water. However, these minerals are typically in the form of calcium carbonate and magnesium carbonate, which are not in a plant available form and cannot be absorbed efficiently by the roots. It is best to remove these minerals present in city water and add in a chelated, readily absorbable form of calcium and magnesium.

< 50 ppm
Fluoride City A hazardous waste product that is present in all municipal water. It is known as a toxic substance to humans and plants. Thirty-four enzymes in plants are affected by fluoride, so enzyme additives will not do their job properly with fluoride in the water.0 ppm
SodiumWell, City
Sodium and other dissolved salts can cause toxicity and dry out plant tissues by impairing their ability to take up water.< 25 ppm
Iron/SulphurWell, City Water containing iron or sulfur may have a metallic taste and an offensive odor. Nutrient lockout, algae growth, and equipment staining can also be results of too much iron in the water.< 0.3 ppm
BacteriaWellGroundwater sources may be affected by animal and human waste and other pathogens. These toxic substances can cause multiple issues in reservoirs and nutrient mixes, be dangerous for human consumption, and contaminate your end-product.0 ppm
Well,City Local agricultural areas may be leaching harmful contaminants into groundwater. These can end up in the water supplied to cultivation facilities and ultimately in plant tissues.0 ppm
Volatile Organic CompoundsCity Some VOCs are known or suspected carcinogens. Trace amounts of these can end up in the plant’s tissues, flowers, and fruits.0 ppm
NitratesCityFound in runoff from agriculture, animal yards, etc., these toxic substances contribute to over-nitrification and algae growth. High quantities of nitrates in untreated water can negatively affect the later stages of flowering, when cultivators typically try to limit nitrate levels.< 5 ppm
pHCityWater that has either too high or too low pH will not allow nutrients to be absorbed properly and can be corrosive to equipment. Adjusting the pH of nutrient solutions may be difficult due to fluctuations in source water levels.6.0 - 8.0
BoronSpringHigh concentrations of boron can cause yellowing or browning of leaves which leads to stunted growth and drastically decreased yields< 0.5 ppm

Using reverse osmosis to filter source water is the single most efficient, economical, and reliable way to ensure the removal of 98 per cent-plus of all contaminants mentioned above.

As reverse osmosis technology continues to advance and new regulations go online, several simplified water filtration solutions for commercial and hobby growers are now available.

These systems ensure consistency and reliability of water input and are critical to the professional grower. Already have access to excellent source water? Consider yourself lucky.

The rest of the country is having to deal with increasingly complex and sometimes dangerous water contamination issues as seen in areas like Flint and Corpus Christi, Texas. Remember, if it’s not healthy for humans, it’s probably not healthy for plants.