Chlorine and Chloramine in Tap Water
UK water suppliers disinfect drinking water to control harmful microorganisms. Free chlorine and chloramine are two treatments hydroponic growers may encounter.
Chlorine
Free chlorine is relatively reactive and may gradually dissipate when water is aerated or left exposed. The speed of removal depends on temperature, concentration, circulation and surface area.
Leaving water overnight should not be treated as a guaranteed method because conditions vary.
Chloramine
Chloramine is more stable than free chlorine and remains in the water for longer. Standing or aeration alone is generally less effective at removing it.
When removal is necessary, use a carbon-filtration system specifically rated for chloramine and provide the required contact time.
Do Disinfectants Harm Hydroponic Plants?
Normal drinking-water disinfectant levels are often tolerated by plants, particularly in mineral-based nutrient systems. Biological growing programmes may be more sensitive because they rely on populations of beneficial bacteria and fungi.
Growers using microbial inoculants, compost teas or biologically active reservoirs should check their local water treatment and follow the biological product manufacturer's instructions.
Hydroponic Water Temperature
Water temperature affects root metabolism, dissolved oxygen and biological activity. As water becomes warmer, its ability to hold dissolved oxygen decreases.
Warm, poorly circulated nutrient solution can stress roots and encourage unwanted microbial growth. Excessively cold water can also slow root activity and nutrient uptake.
Possible Signs of Excessive Water Temperature
- Reduced dissolved oxygen
- Slow or stressed plant growth
- Brown, soft or slimy roots
- Unpleasant reservoir odours
- Rapid biofilm or microbial growth
- Water warming significantly during the light period
Ways to Control Water Temperature
- Keep reservoirs away from direct light
- Use opaque and insulated tanks
- Insulate exposed pipes and irrigation lines
- Improve room-temperature control
- Maintain water circulation
- Position heat-producing pumps outside the reservoir where practical
- Use a correctly sized water chiller when required
A water chiller should not be used as a substitute for correcting excessive room temperatures, direct radiant heat or poor reservoir positioning.
Hydroponic Reservoir Management
A well-managed reservoir should remain mixed, protected from light and easy to inspect. It should also provide suitable circulation and oxygenation for the system being used.
In a recirculating system, every plant shares the same nutrient solution. A small reservoir problem can therefore spread throughout the entire crop.
Daily Reservoir Checks
- Water level
- EC or nutrient strength
- pH
- Water temperature
- Pump operation
- Aeration where used
- Leaks and blocked lines
- Water clarity and odour
- Root colour and texture
Understanding Changes in EC
Plants do not always absorb water and mineral nutrients at the same rate.
| Observation |
Possible Meaning |
Suggested Response |
| Water level falls and EC rises |
Plants may be taking proportionally more water than nutrients |
Consider topping up with plain or lightly adjusted water and review feed strength |
| Water level falls and EC falls |
Plants may be taking nutrients readily or the solution may be becoming diluted |
Review nutrient strength, plant demand and top-up strategy |
| Water level falls and EC remains stable |
Water and nutrient uptake may be reasonably balanced |
Continue monitoring and maintain the reservoir |
These patterns provide useful clues but should always be interpreted alongside crop stage, environmental conditions, root health and meter accuracy.
How Often Should the Reservoir Be Changed?
There is no universal replacement schedule. The correct interval depends on reservoir size, crop demand, system design, water quality, nutrient formulation and the number of plants sharing the solution.
Small reservoirs may experience rapid changes, while large, correctly managed reservoirs can remain stable for longer.
Preventing Algae
Algae requires light, water and nutrients. The most effective control is to prevent light from entering the reservoir, irrigation channels and wet growing media.
- Use opaque reservoirs and lids
- Cover exposed growing media
- Repair light leaks
- Clean channels and surfaces between crops
- Avoid clear pipework in illuminated areas
Common Hydroponic Water Problems
Unstable pH
Possible causes include high alkalinity, microbial activity, unsuitable nutrient mixing, a small reservoir, incorrect calibration or rapid plant uptake.
High Starting EC
This may indicate a high concentration of dissolved minerals. A water report or laboratory analysis is needed to identify which minerals are present.
Cloudy Water
Cloudiness may be caused by incompatible nutrient products, microbial growth, organic material, precipitation or contamination.
Salt and Scale
White deposits may develop because of hard water, evaporation, excessive nutrient concentration or insufficient irrigation-system maintenance.
Biofilm
Slippery deposits on reservoir walls and pipework can restrict water flow and provide a habitat for unwanted microorganisms.
Blocked Drippers
Emitters may become blocked by mineral scale, precipitated nutrients, organic additives, debris or biological growth.
Brown Roots
Brown roots are not always diseased. Nutrient dyes and organic additives may stain healthy roots, so also examine their texture, smell and overall plant health.
Unpleasant Odour
A sour, stagnant or rotten smell may indicate low oxygen, decaying organic matter, excessive temperature or unwanted microbial activity.
Understanding Your Water-Quality Report
Most UK water suppliers publish water-quality information for each supply area. This can help growers understand the minerals and compounds present before selecting nutrients or treatment equipment.
Published figures may be shown as averages, ranges or individual test results. Water quality can also change seasonally, so the report should be treated as a useful guide rather than an exact live reading from your tap.
| Measurement |
Why It Matters in Hydroponics |
| Calcium |
Contributes to hardness and plant nutrition. Excessive levels may affect nutrient balance and produce scale. |
| Magnesium |
Essential for chlorophyll and photosynthesis. It also contributes to total water hardness. |
| Sodium |
High concentrations can contribute to salinity and interfere with potassium and water uptake. |
| Bicarbonates |
Increase alkalinity and resistance to pH adjustment. High levels may cause repeated upward pH drift. |
| Total Hardness |
Usually represents the combined concentration of calcium and magnesium. |
| Iron |
Required in small amounts, but elevated concentrations may stain equipment or contribute to blockages. |
| Manganese |
An essential micronutrient at low levels, but excessive concentrations are undesirable. |
| Sulphate |
Contributes sulphur and forms part of the total dissolved mineral content. |
| Nitrate |
Contributes nitrogen and should be considered when evaluating the starting water. |
| Chloride |
Required only in small amounts. Excessive chloride can contribute to salinity problems. |
| TDS or EC |
Provides a general indication of the total dissolved mineral concentration. |
| pH |
Shows the water's acidity or alkalinity at the time of testing, but does not reveal its buffering strength. |
Calcium
Calcium supports cell-wall development, root growth and healthy new plant tissue. Tap water in hard-water areas may already supply a meaningful amount.
This can reduce the need for calcium supplementation, but excessive calcium may contribute to scale or interfere with the intended nutrient balance.
Magnesium
Magnesium forms the central component of chlorophyll and is essential for photosynthesis. Naturally occurring magnesium contributes to plant nutrition and total hardness.
Sodium
Sodium is not required in significant amounts by most hydroponic crops. High concentrations may increase salinity and interfere with potassium uptake and water movement within the plant.
Bicarbonates and Alkalinity
Bicarbonates are among the most important figures on a hydroponic water report. They resist acidification and increase the amount of pH Down needed to adjust the solution.
High bicarbonate levels can cause repeated upward pH drift even when the initial pH has been adjusted correctly.
Temporary and Permanent Hardness
Temporary hardness is primarily associated with bicarbonates. Permanent hardness is associated with compounds such as calcium sulphate and magnesium sulphate that remain after heating.
This distinction helps explain why some supplies produce heavy limescale while others have a high mineral content but behave differently.
Expert Tip: Do not judge source water by EC alone. Two water supplies with the same EC can behave very differently because the dissolved minerals may be completely different.
When to Arrange a Laboratory Water Analysis
- Persistent problems continue despite apparently correct pH and EC
- Borehole or collected water is being used
- High sodium, iron or bicarbonates are suspected
- Source-water quality changes significantly throughout the year
- A commercial facility requires repeatable records
- A precise custom nutrient formulation is being developed
Choosing Water for Different Hydroponic Systems
Deep Water Culture
In Deep Water Culture, roots remain submerged in the nutrient solution. Water temperature, dissolved oxygen, reservoir cleanliness, EC and pH stability are therefore especially important.
Nutrient Film Technique
NFT systems circulate a shallow film of nutrient solution through growing channels. Relatively small reservoir volumes can change quickly as crops mature, making regular monitoring essential.
Drip Irrigation
Drip systems rely on small emitters that can be affected by mineral scale, debris, precipitated nutrients and biological material. Filtration and irrigation-line maintenance are particularly important.
Flood and Drain
Flood-and-drain systems repeatedly circulate the same solution through the root zone. Reservoir hygiene, drainage and pump reliability help prevent contaminants from being distributed throughout the system.
Aeroponics
Aeroponic nozzles have small openings and may be vulnerable to blockages. Well-filtered source water, routine flushing and careful nutrient selection can improve reliability.
Coco Coir
Coco is commonly managed as a hydroponic growing medium. Hard water may already contribute calcium and magnesium, while RO or very soft water may require suitable supplementation.
Monitoring feed and run-off EC can help identify salt accumulation and irrigation problems.
Run-to-Waste Systems
Run-to-waste systems do not return drainage to the main nutrient tank, reducing the accumulation of plant exudates and changing nutrient ratios. Source-water quality still influences the feed, emitters and growing medium.
Seasonal Changes in Tap Water
Growers often assume tap water remains identical throughout the year. In reality, water suppliers may change between reservoirs, rivers, boreholes and treatment works according to rainfall, demand and maintenance requirements.
Seasonal changes may affect:
- Starting EC
- Hardness
- Bicarbonate concentration
- Sodium concentration
- pH
- Chlorine or chloramine treatment
If a previously stable nutrient programme becomes difficult to manage, retest the source water before changing nutrients or adding extra supplements.
Signs That Water Quality May Be Causing Problems
- Repeated pH drift
- Unexpectedly high starting EC
- Slow or inconsistent growth
- Pale or distorted new leaves
- Leaf-tip damage despite moderate nutrient strength
- Mineral deposits around emitters and tanks
- Blocked irrigation equipment
- Cloudy nutrient solution
- Unhealthy roots or reservoir odours
- Different plant responses despite receiving the same feed
These symptoms may also have other causes. Check meter calibration, environmental conditions, irrigation frequency, root-zone health and nutrient mixing before concluding that the source water is responsible.
Hydroponic Water Testing Checklist
Before Adding Nutrients
- Measure source-water EC
- Check water temperature
- Identify whether the water is hard, soft or RO
- Inspect water clarity and odour
- Check the condition of filters
- Confirm meters have been calibrated
After Mixing Nutrients
- Confirm products were added separately
- Mix the reservoir thoroughly
- Measure the final EC
- Allow the solution to stabilise
- Measure and adjust pH
- Check for cloudiness or sediment
During Daily Use
- Record reservoir level
- Record EC
- Record pH
- Record water temperature
- Inspect pumps and air stones
- Check roots and irrigation flow
Routine Maintenance
- Clean filters and strainers
- Inspect irrigation lines
- Remove algae
- Check pump performance
- Service water-treatment equipment
- Replace filters when required
Keeping written records makes trends much easier to identify. A simple grow diary can reveal changes in source water, crop demand and reservoir behaviour before they become serious problems.
Choosing the Right Water-Treatment Approach
Use Tap Water When
- The starting EC is manageable
- Water hardness suits the nutrient range
- pH remains reasonably stable
- Scale is limited
- Plants are performing consistently
Consider Carbon Filtration When
- Chlorine affects a biological programme
- Chloramine removal is required
- Sediment is present
- The water has an undesirable smell or taste
- RO membrane protection is needed
Consider RO Water When
- The starting EC is excessively high
- Bicarbonates make pH difficult to manage
- Sodium is elevated
- Scale repeatedly damages equipment
- Greater nutritional precision is needed
Arrange a Water Analysis When
- Problems remain unexplained
- Borehole water is used
- Water quality changes seasonally
- A commercial nutrient recipe is being developed
- Accurate compliance records are required
Common Hydroponic Water Myths
Myth: Reverse Osmosis Water Is Always Better
RO water is not automatically better. Suitable tap water can produce excellent results while supplying useful calcium, magnesium and buffering capacity.
Myth: High EC Always Means Bad Water
A high EC means the water contains more dissolved ions. Whether that is a problem depends on which minerals are present and the needs of the nutrient programme.
Myth: Leaving Water Overnight Removes Every Disinfectant
Free chlorine may dissipate under suitable conditions, but chloramine is more stable and generally requires appropriate filtration when removal is necessary.
Myth: Plain-Water pH Is the Most Important Reading
The pH of untreated water provides limited information. Starting EC, alkalinity, bicarbonates, hardness and mineral composition may be more useful when predicting how the nutrient solution will behave.
Myth: More CalMag Is Always Beneficial
Calcium and magnesium are essential, but excessive supplementation can create nutrient imbalances. Consider the source water and base nutrient before adding extra products.
Myth: Brown Roots Always Mean Root Rot
Some nutrients and biological additives stain roots. Healthy roots should also be assessed by their firmness, smell, branching and the condition of the plant.
Water Quality Best Practices
- Test the source water before mixing nutrients.
- Understand the difference between hardness and alkalinity.
- Use nutrients designed for your water type.
- Measure EC and pH with calibrated meters.
- Keep reservoirs clean, covered and protected from light.
- Maintain stable water temperature and circulation.
- Record readings so gradual changes are easy to identify.
- Use filtration or RO only when there is a clear reason.
- Investigate the water before automatically increasing feed strength.
The best hydroponic water is not necessarily the purest water. It is water that is understood, correctly treated when necessary and matched to the crop, system and nutrient programme.
Frequently Asked Questions
Is tap water suitable for hydroponics?
Yes. Tap water is suitable for many hydroponic growers. Its starting EC, hardness, alkalinity and mineral composition should be considered when selecting nutrients and supplements.
What is the best water for hydroponics?
There is no single best water for every system. Suitable tap water is convenient and may supply useful minerals, while RO water provides greater control when the source water is excessively hard, saline or inconsistent.
Should I use reverse osmosis water?
RO water is worth considering when the source-water EC, bicarbonate, sodium or hardness levels interfere with nutrient management. It may be unnecessary when the tap water already performs well.
Does RO water need CalMag?
RO water contains very little calcium or magnesium, so supplementation may be necessary. The requirement depends on the base nutrient, crop and growing medium.
What starting EC is suitable for hydroponic water?
A lower starting EC gives greater control over the final nutrient solution, but there is no universal maximum suitable for every crop or nutrient range. A water analysis is more informative than EC alone because it identifies the individual minerals present.
What is water hardness?
Water hardness primarily describes the amount of dissolved calcium and magnesium. Hard water can be used successfully when it is matched with an appropriate nutrient formulation.
What is water alkalinity?
Alkalinity describes the water's ability to neutralise acid and resist a reduction in pH. In tap water, it is commonly associated with bicarbonates.
What pH should hydroponic water be?
The suitable pH depends on the crop, growing medium and nutrient system. Most hydroponic programmes use a mildly acidic nutrient solution. Follow the range recommended by the nutrient manufacturer and adjust pH after nutrients have been mixed.
Why does my reservoir pH keep rising?
Rising pH may be caused by high bicarbonate alkalinity, plant nutrient uptake, microbial activity, evaporation, top-up water or reservoir conditions. Check meter calibration and source-water alkalinity before repeatedly adding more acid.
Why does my reservoir pH keep falling?
Falling pH may result from nutrient uptake patterns, biological activity, root problems, excessive acid addition or unstable water with little buffering capacity.
Does chlorine harm hydroponic plants?
Normal drinking-water chlorine levels are often tolerated by plants. Biological programmes that rely on beneficial microorganisms may be more sensitive.
What is chloramine?
Chloramine is a stable disinfectant created by combining chlorine and ammonia. It remains in water longer than free chlorine and generally requires suitable carbon filtration when removal is needed.
Can I leave tap water overnight to remove chlorine?
Some free chlorine may dissipate when water is exposed and aerated, but the result depends on the conditions. Chloramine is more persistent and is not reliably removed by standing overnight.
Can rainwater be used for hydroponics?
Yes, provided it is collected safely, filtered, stored correctly and tested before use. Roof-collected rainwater may contain debris, microorganisms, bird waste or contaminants from roofing materials.
Why is water temperature important?
Water temperature affects dissolved oxygen, root metabolism and microbial activity. Warm water holds less oxygen and may increase root stress, while excessively cold water can slow nutrient uptake.
Do I need a water chiller?
A chiller may be useful when reservoir temperatures regularly become excessive and cannot be controlled through reservoir positioning, insulation or room cooling. It is not essential for every hydroponic system.
How often should I change my reservoir?
The correct interval depends on reservoir volume, crop demand, system design, nutrient programme and water quality. Monitor EC, pH, temperature, clarity and plant health rather than relying on a single fixed schedule.
Should I top up with plain water or nutrient solution?
Base the decision on the reservoir level and EC trend. When EC rises as water is consumed, plain or lightly adjusted water may be appropriate. When EC falls, additional nutrients may be required.
Why is my hydroponic water cloudy?
Cloudiness may be caused by microbial growth, organic material, incompatible additives, nutrient precipitation or contamination. Inspect the solution, roots, temperature and mixing procedure before using it.
Why are my hydroponic roots brown?
Nutrients and organic additives can stain healthy roots. Brown roots accompanied by softness, slime, poor smell and declining plant health may indicate a root-zone problem requiring investigation.
How can I find my local water-quality report?
Most UK water suppliers provide a postcode-based water-quality report on their website. Look for hardness, calcium, magnesium, sodium, nitrate, chloride and pH figures. A laboratory test may be needed for detailed bicarbonate or alkalinity information.
Continue Learning
Water quality is closely connected to nutrients, pH, EC, irrigation and root-zone management. Continue your learning with these Doctor Blooms Academy guides:
- Hydroponic Nutrients Explained
- pH and EC Explained -- coming soon
- Hydroponic Grow Media Explained -- coming soon
- Hydroponic Systems Explained -- coming soon
