Your water is the base every feed is built on, and US tap is anything but consistent. Hardness swings by region, and most supplies carry chlorine or chloramine to keep them safe to drink. Filtering that water is the cheapest way to turn an unknown starting point into a clean, repeatable one you can dial in the same way every grow.

Why filter your water at all

US tap water varies enormously from one region to the next. Hard water arrives loaded with dissolved calcium and magnesium, a background EC and a raised pH before you have added a single nutrient. Soft water gives you almost none of that. Two growers running the identical feed chart on different taps can get completely different results, purely because their starting water is not the same.

On top of hardness, nearly all mains water is dosed with chlorine or chloramine. Both are there to kill microbes in the pipe, and both can knock back the beneficial biology in an organic or living root zone. Chlorine at least off-gasses if you let water stand or run it through carbon. Chloramine does not, which we come back to below.

A filtered, zero-EC start solves the root problem. When every element in the tank is one you put there on purpose, your feed becomes repeatable, and that consistency is exactly what a proper nutrient schedule is built around.

Clean water is the foundation of a stable system. This collection is part of our Hydroponic Systems & Water Management guide, which covers how it fits the rest of your setup.

Reverse osmosis: the cleanest, most repeatable start

A reverse-osmosis (RO) unit forces your tap through a semi-permeable membrane that blocks dissolved salts and the bulk of contaminants, leaving water at close to zero EC and a neutral pH. That is the cleanest start you can give a feed, because you build the whole recipe from scratch knowing nothing was already in the water.

Size an RO unit by its GPD rating, the gallons per day it can make. The number in the name is your guide: a Hydro-Logic Stealth RO 150 makes far less per day than a Stealth RO 300, and the Evolution RO1000 is built for high-volume rooms. Match the daily output to how fast you fill your reservoir, then allow some headroom, because RO is slow by nature and you do not want to be waiting on it before every feed.

Two things to plan for. First, an RO unit sends a share of your tap to drain as waste water alongside the clean permeate; higher-efficiency units improve that ratio, but some waste is unavoidable. Second, RO strips calcium and magnesium out along with everything else, so on RO water a cal-mag supplement stops being optional and becomes essential. Budget for it from the start.

Pre-filters, chloramine and simple dechlorinators

Every RO membrane needs protecting. Sediment and carbon pre-filters, the Hydro-Logic Tall Boy and Big Boy ranges, sit ahead of the membrane: the sediment stage catches grit that would clog it, and the carbon stage strips the chlorine that would otherwise degrade it. Run them and the membrane lasts far longer; skip them and you replace an expensive part early.

Chloramine is the exception worth knowing. Unlike chlorine, it does not off-gas when water stands, and a standard carbon filter only partly removes it. If your supplier uses chloramine, you need a filter built for it, such as the Hydro-Logic ChloraShield, which swaps into the Big Boy, Tall Boy and Stealth housings.

Not everyone needs full RO. If your tap is reasonably soft and your only real problem is chlorine, a simple inline dechlorinator like the Tall Boy or Big Boy De-Chlorinator cleans the water without the waste, the cost or the cal-mag dependency of RO. Match the tool to the problem you actually have.

Choosing the right water treatment

Option	Removes	Best for
Reverse osmosis unit (Stealth RO, Evolution RO)	Almost everything: salts, chlorine, most contaminants, down to near-zero EC	A clean, repeatable start on hard or unpredictable tap
Carbon & sediment pre-filter (Tall Boy, Big Boy)	Sediment, chlorine, taste & odor	Protecting an RO membrane, or clean-up on decent tap
ChloraShield carbon filter	Chloramine, which standing water will not shift	Areas dosed with chloramine rather than chlorine
Inline dechlorinator (Tall Boy / Big Boy De-Chlorinator)	Chlorine and sediment	Simple treatment where full RO is not needed

Water filtration & RO units we stock

Frequently asked questions