Tap water, hard water and filters: what an indoor garden needs

Most indoor gardens, Gardyn included, run well on ordinary tap water. Gardyn's help center recommends tap water, says its plant food and HydroBoost water treatment handle pH, and asks you to avoid water from a household softener. Filtered, reverse osmosis or distilled water also works, with a calcium and magnesium supplement added.

Water questions come up early for most new growers, often because older hydroponics advice calls for testing kits and special water. This guide sorts out what actually matters: chlorine, hardness, pH, softeners and filters, and when it makes sense to switch water types.

Key takeaways

• Tap water is the recommended source for a Gardyn. You do not need a special water supply.
• Hard water is fine. Most tap and well water falls in the standard to hard range, and Gardyn's dosing guidance accounts for it.
• Avoid water from a household water softener, which adds sodium. Naturally soft water is a different thing and is acceptable.
• You do not need to test pH in a Gardyn. Plant food and HydroBoost are formulated to bring the water into the right range.
• If you use filtered, reverse osmosis (RO) or distilled water, add CAL-MAG, because those waters are missing minerals plants use.

Is tap water OK for an indoor garden?

Yes. Gardyn's help center names tap water as the recommended source and explains that tap water chemistry varies by location, so Gardyn's plant food and HydroBoost are designed to balance a range of tap waters and plant varieties. Your routine stays the same wherever you live: follow the plant food guidelines, top off weekly, add HydroBoost and refresh the tank monthly.

What about chlorine and chloramine? Many water utilities disinfect with chlorine, and others use chloramine. The EPA explains that chloramines are most commonly formed by adding ammonia to chlorine and that they provide long-lasting protection because they "do not break down quickly in water pipes." That long life means chloramine lingers in tap water longer than chlorine does.

Gardyn's help center does not call for pre-treating tap water, so you can fill straight from the faucet. If you want to know which disinfectant your utility uses, check its annual water quality report (more on that below).

What does hard water mean for an indoor garden?

Hardness is a measure of dissolved minerals, mainly calcium and magnesium. The US Geological Survey groups water into four classes, measured in milligrams per liter (mg/L) as calcium carbonate:

Calcium and magnesium are nutrients plants use, and Gardyn's help center says standard to hard tap water is fine to use. Its main side effect is mineral buildup. The USGS notes that hardness can cause scaling in equipment, which in a garden shows up as white crust on surfaces that stay wet. Gardyn's help center notes that weekly HydroBoost helps reduce nutrient and salt deposits.

Gardyn's water type guide lists two everyday signs of hard water: mineral spots on dishes and a slimy feeling on your hands after washing with soap.

How do you find your water's hardness? You have two easy options:

1. Read your water quality report. The EPA requires community water systems to deliver a Consumer Confidence Report to customers each year by July 1. Gardyn's help center notes that hardness is often measured and reported annually, so your utility's report or customer service can tell you.
2. Use a test kit. Gardyn's help center notes that hardness test kits are sold at home improvement stores.

If you are not sure, Gardyn's HydroBoost guide says to start with the standard dose for at least a month. If root health or cleanliness does not improve, increase by 1 teaspoon at a time, up to the hard water dose.

Why is softened water a problem?

A household water softener removes hardness by swapping calcium and magnesium for sodium. Gardyn's help center says softened water is not recommended because most softeners use sodium chloride, which can build up in the garden and harm plants. Use untreated municipal water instead.

This lines up with university guidance. Penn State's College of Agricultural Sciences explains that plants need only tiny amounts of sodium and that it becomes harmful over time. In a recirculating tank, sodium has nowhere to go, so it accumulates between refreshes.

If your whole house is on a softener, check whether a kitchen tap or an outdoor spigot bypasses it. Some homes have an unsoftened line. If not, ask Gardyn support about using filtered or RO water instead.

Do you need to test or adjust pH?

In a Gardyn, no. pH measures how acidic or basic water is on a scale from 0 to 14, with 7 as neutral. It matters because it affects which nutrients plants can absorb. Drinking water is generally kept at a higher pH than hydroponic plants prefer. The EPA's secondary standard for drinking water pH is 6.5 to 8.5, while Oklahoma State University Extension recommends a hydroponic nutrient solution pH between 5 and 6.

Gardyn closes that gap for you, which is one of the ways Gardyn simplifies hydroponics. The help center says its plant food and HydroBoost are formulated to create an ideal pH, so you do not need to measure it. HydroBoost lowers pH as part of its job. If you want the background on why pH and nutrient strength matter in hydroponics, read our guide to pH and EC in hydroponics.

Should you use a filter, RO or distilled water?

All three work in a Gardyn, though none is required. Here is how the common options compare, based on the EPA's home water treatment guide and Gardyn's help center.

Why add CAL-MAG? RO and distilled water strip out the calcium and magnesium plants use. Plants take up those minerals dissolved in water, a process our post on mineral and organic plant food explains. Gardyn's help center recommends 1 teaspoon of CAL-MAG per gallon weekly when you use naturally soft, filtered or distilled water, added after the other nutrients during your weekly top-off or refresh. For HydroBoost, use the lower filtered water dose.

When does switching make sense? Consider filtered, RO or distilled water if your home only has softened water, if heavy mineral crust keeps returning even on the hard water HydroBoost dose. Keep in mind that RO systems send some water down the drain. The EPA notes that WaterSense labeled RO models generate 2.3 gallons of waste water or less for every gallon treated.

If you buy a filter, the EPA recommends choosing one certified to the standard that matches your goal and checking the performance data sheet for the specific contaminant you care about.

A quick note on refilling. When you refill during a refresh, Gardyn's help center describes mixing tap water with the plant food dose one gallon at a time in a clean container, which keeps the mix even.

Ready to see how the water system keeps plants fed? See how Gardyn works.

Frequently asked questions

Can I use tap water in a hydroponic garden?

Yes. Gardyn's help center recommends tap water and says its plant food and HydroBoost are designed to balance a range of tap water types.

Is hard water bad for an indoor garden?

No. Most tap and well water is standard to hard, and Gardyn's guidance covers it. Hard water can leave mineral crust, which weekly HydroBoost and regular refreshes help limit.

Can I use water from my water softener?

Gardyn recommends against it. Most softeners add sodium, which builds up in the tank and can harm plants. Naturally soft water is acceptable with CAL-MAG added.

Do I need to check the pH of my water?

Not in a Gardyn. The plant food and HydroBoost are formulated so you do not have to test or adjust pH.

Should I use distilled water in my Gardyn?

You can. Add 1 teaspoon of CAL-MAG per gallon weekly and use the filtered water HydroBoost dose, since distilled water has no minerals.