Water Quality and Treatment
Expert-defined terms from the Professional Certificate in Water Conservation Rainwater Harvesting course at London School of Business and Administration. Free to read, free to share, paired with a professional course.
Alkalinity – Related terms #
pH, buffering capacity. Alkalinity measures the water’s ability to neutralize acids, primarily contributed by bicarbonate, carbonate, and hydroxide ions. Example: a rainwater tank with 150 mg/L alkalinity resists pH swings. Practical application: adjusting alkalinity before disinfection to stabilize pH. Challenge: high alkalinity may require additional treatment steps to meet specific reuse standards.
Ammonia – Related terms #
nitrogen, nitrification. Ammonia (NH₃) is a toxic nitrogen compound formed from organic decay or fertilizer runoff. Example: leachate from garden soils can raise ammonia levels in harvested rainwater. Practical application: biological filters such as trickling filters convert ammonia to nitrate. Challenge: low-temperature conditions slow nitrification, necessitating supplemental treatment.
Biological Oxygen Demand – Related terms #
BOD, organic load. BOD quantifies the amount of dissolved oxygen needed by microorganisms to decompose organic matter in water over five days. Example: a BOD of 10 mg/L indicates moderate organic contamination. Practical application: using BOD as a design parameter for pond aeration systems. Challenge: high BOD can lead to oxygen depletion, harming aquatic life and reducing treatment efficiency.
Brine – Related terms #
reverse osmosis concentrate, waste stream. Brine is the high‑salinity waste generated during desalination or reverse osmosis (RO) processes. Example: a 2 g/L brine from an RO unit used for rainwater polishing. Practical application: brine may be diluted and discharged or evaporated for salt recovery. Challenge: managing brine volume in small‑scale rainwater systems where disposal options are limited.
Carbonate Hardness – Related terms #
temporary hardness, scaling. Carbonate hardness arises from calcium and magnesium ions paired with carbonate or bicarbonate, dissolving at higher pH. Example: 80 mg/L carbonate hardness in a rooftop catchment. Practical application: pre‑treatment with acid dosing reduces scaling in storage tanks. Challenge: over‑acidification can lower pH excessively, affecting downstream disinfection.
Chlorination – Related terms #
free chlorine, chloramine. Chlorination introduces chlorine to inactivate pathogens, typically as hypochlorous acid. Example: maintaining 0.5 mg/L free chlorine in a community rainwater system. Practical application: automatic dosing pumps deliver consistent residual. Challenge: chlorine can react with organic matter to form trihalomethanes, requiring careful dose control.
Coagulation – Related terms #
flocculation, turbidity removal. Coagulation adds chemicals (e.g., alum) to destabilize suspended particles, forming larger aggregates. Example: alum dose of 20 mg/L reduces turbidity from 30 NTU to below 5 NTU. Practical application: upstream of sediment filters in rainwater treatment trains. Challenge: improper dosing leads to excess sludge or insufficient particle removal.
Conductivity – Related terms #
total dissolved solids, ion concentration. Conductivity measures water’s ability to conduct electricity, reflecting dissolved ion levels. Example: 250 µS/cm indicates moderate mineral content in harvested rainwater. Practical application: conductivity sensors provide real‑time monitoring for treatment adjustments. Challenge: high conductivity may signal contamination requiring additional filtration.
Disinfection By‑Products – Related terms #
trihalomethanes, haloacetic acids. Disinfection by‑products (DBPs) form when chlorine reacts with natural organic matter. Example: trihalomethane levels of 70 µg/L in a treated rainwater supply. Practical application: employing UV or ozone reduces DBP formation. Challenge: balancing pathogen control with DBP limits in potable standards.
Distillation – Related terms #
thermal desalination, vapor condensation. Distillation heats water to vapor, then condenses it, leaving most contaminants behind. Example: solar stills producing 2 L/day of distilled rainwater. Practical application: small‑scale production of high‑purity water for laboratory use. Challenge: high energy demand and slow production rates limit scalability.
Effluent – Related terms #
outflow, discharge. Effluent refers to water exiting a treatment system, often after quality improvement. Example: effluent from a sand filter meeting 5 NTU turbidity criteria. Practical application: monitoring effluent quality ensures compliance with local regulations. Challenge: varying influent quality can cause effluent fluctuations, requiring adaptive control.
Electrodialysis – Related terms #
ion exchange membranes, desalination. Electrodialysis uses an electric field to move ions through selective membranes, separating salts from water. Example: removing 80 % of dissolved salts from rainwater harvested in coastal areas. Practical application: compact units for residential water polishing. Challenge: membrane fouling and high electrical costs in low‑flow scenarios.
EPA Standards – Related terms #
regulatory limits, drinking water criteria. EPA standards define permissible levels of contaminants in public water supplies. Example: lead limit of 15 ppb for potable rainwater. Practical application: designing treatment trains to meet or exceed these benchmarks. Challenge: updating designs as standards evolve, especially for emerging contaminants.
Filtration – Related terms #
media filter, cartridge filter. Filtration removes suspended particles by passing water through a porous medium. Example: a 5 µm cartridge filter reducing turbidity from 15 NTU to 1 NTU. Practical application: first‑line barrier in rainwater harvesting systems. Challenge: filter clogging requires routine maintenance and replacement.
Flocculation – Related terms #
coagulation, gentle mixing. Flocculation gently agitates coagulated water to encourage formation of larger flocs. Example: slow mixing at 30 rpm for 15 minutes after alum dosing. Practical application: enhances sedimentation efficiency in large tanks. Challenge: excessive mixing can break flocs, reducing removal performance.
Hardness – Related terms #
temporary hardness, permanent hardness. Hardness quantifies calcium and magnesium concentrations, expressed as mg/L CaCO₃. Example: 180 mg/L hardness indicating moderately hard rainwater. Practical application: softening via ion exchange before domestic use to prevent scale. Challenge: high hardness increases soap consumption and may damage appliances.
Hydraulic Retention Time – Related terms #
HRT, residence time. Hydraulic retention time (HRT) is the average time water spends in a treatment unit. Example: 4‑hour HRT in a sand filter for optimal particle settling. Practical application: sizing tanks to achieve required treatment levels. Challenge: short HRTs can lead to incomplete removal of contaminants.
Ion Exchange – Related terms #
resin, softening. Ion exchange swaps undesirable ions (e.g., calcium) with more benign ones (e.g., sodium) using resin beads. Example: a cation‑exchange column reducing hardness from 200 mg/L to 20 mg/L. Practical application: producing soft water for irrigation and household appliances. Challenge: resin regeneration generates brine that must be managed responsibly.
Lead – Related terms #
heavy metals, plumbing corrosion. Lead is a toxic metal that can leach from old pipes into stored rainwater. Example: 8 ppb lead detected in a rooftop tank after a month of storage. Practical application: using lead‑free fittings and periodic water testing. Challenge: low‑level contamination may be hard to detect without sensitive analytical methods.
Microfiltration – Related terms #
MF membranes, pore size. Microfiltration employs membranes with pore sizes 0.1–10 µm to remove bacteria and turbidity. Example: a 0.2 µm MF unit achieving 99.9 % bacterial removal. Practical application: pre‑treatment before UV disinfection in rainwater systems. Challenge: membrane fouling by organic matter necessitates regular cleaning.
Monitored Parameters – Related terms #
sensor suite, data logging. Monitored parameters are measurable water quality indicators such as pH, temperature, and turbidity. Example: continuous pH monitoring showing values between 6.8 and 7.2. Practical application: automated control systems adjust dosing based on real‑time data. Challenge: sensor drift and calibration requirements increase operational complexity.
Nanofiltration – Related terms #
NF membranes, divalent ion rejection. Nanofiltration uses membranes with 0.001–0.01 µm pores to reject divalent ions and larger organic molecules. Example: NF reducing hardness by 70 % while retaining beneficial minerals. Practical application: polishing step after RO for rainwater intended for irrigation. Challenge: higher pressure requirements than MF, increasing energy consumption.
Ozone Treatment – Related terms #
oxidation, advanced oxidation. Ozone (O₃) is a powerful oxidant used to disinfect and break down organic contaminants. Example: ozone dose of 0.8 mg/L achieving 4‑log bacterial inactivation. Practical application: reducing DBP formation compared with chlorine. Challenge: ozone generators are costly and ozone must be fully decomposed before consumption.
pH – Related terms #
acidity, alkalinity. pH indicates the hydrogen ion concentration, ranging from 0 (acidic) to 14 (alkaline). Example: rainwater pH of 5.5 due to atmospheric CO₂. Practical application: adjusting pH to optimal levels for coagulant performance. Challenge: fluctuations can affect metal solubility and disinfection efficacy.
Permeate – Related terms #
treated water, membrane output. Permeate is the clean water that passes through a membrane during processes like RO or NF. Example: RO permeate with 0.5 NTU turbidity and 30 µS/cm conductivity. Practical application: final product for potable use after rainwater pre‑treatment. Challenge: permeate flow declines over time due to fouling, requiring periodic cleaning.
Phytoremediation – Related terms #
plant uptake, constructed wetlands. Phytoremediation employs plants to absorb or transform contaminants from water. Example: cattail beds reducing nitrate concentrations by 40 % in a rainwater runoff channel. Practical application: low‑cost polishing of harvested rainwater before storage. Challenge: seasonal plant growth limits continuous performance.
Point of Use Treatment – Related terms #
POU, final stage. Point of use (POU) treatment occurs at the tap or appliance, delivering the final quality boost. Example: a UV POU unit delivering 99.99 % viral inactivation for household drinking water. Practical application: providing an extra safety layer for stored rainwater. Challenge: ensuring consistent power supply and maintenance at the consumer end.
Potable Water Standards – Related terms #
drinking water guidelines, WHO limits. Potable water standards define acceptable contaminant levels for safe consumption. Example: WHO guideline for arsenic at 10 µg/L. Practical application: designing rainwater treatment to meet these limits before distribution. Challenge: multiple standards may apply simultaneously, complicating compliance.
Pre‑chlorination – Related terms #
oxidative pre‑treatment, chlorine demand. Pre‑chlorination adds chlorine before filtration to control biological growth on media. Example: 0.2 mg/L chlorine dose before sand filtration reducing biofilm formation. Practical application: extending filter life in rainwater tanks. Challenge: excess chlorine can increase DBP formation later in the process.
Primary Treatment – Related terms #
screening, gross removal. Primary treatment removes large debris and coarse particles through screens and sedimentation. Example: a 1 mm screen catching leaves and insects from rooftop runoff. Practical application: protecting downstream equipment from clogging. Challenge: does not address dissolved contaminants, requiring additional treatment steps.
Quality Assurance – Related terms #
QA, verification. Quality assurance (QA) involves systematic procedures to ensure treatment processes meet design specifications. Example: monthly calibration of turbidity meters as part of a QA program. Practical application: maintaining consistent water quality for certification purposes. Challenge: resource‑intensive documentation and staff training.
Radon – Related terms #
radioactive gas, decay product. Radon is a naturally occurring radioactive gas that can dissolve in groundwater and rainwater. Example: radon levels of 150 Bq/L in a basement rainwater storage tank. Practical application: aeration or degassing units to reduce radon before consumption. Challenge: radon mitigation adds complexity to small‑scale systems.
Rapid Sand Filter – Related terms #
gravity filter, backwash. A rapid sand filter uses coarse sand and high flow rates to remove suspended solids quickly. Example: a 2‑m³ rapid sand filter achieving 5 NTU turbidity after 30 minutes. Practical application: intermediate treatment after coarse screening in rainwater plants. Challenge: frequent backwashing needed to prevent clogging, increasing water usage.
Reactor – Related terms #
treatment tank, contact chamber. A reactor is a vessel where chemical, biological, or physical processes occur. Example: a 500‑L chlorine contact reactor ensuring 30‑minute exposure for disinfection. Practical application: providing sufficient contact time for pathogen kill. Challenge: maintaining uniform mixing and temperature control.
Reverse Osmosis – Related terms #
RO, high‑pressure membrane. Reverse osmosis forces water through a semi‑permeable membrane, rejecting salts, microbes, and many organics. Example: RO system producing 0.2 L/min permeate with 0.05 mg/L total dissolved solids. Practical application: polishing rainwater for high‑purity applications such as laboratory work. Challenge: high energy demand and brine disposal in remote rainwater installations.
Salinity – Related terms #
salt content, electrical conductivity. Salinity denotes the concentration of dissolved salts, often expressed in ‰ or mg/L. Example: coastal rainwater with 600 mg/L total dissolved solids. Practical application: assessing suitability for irrigation versus potable use. Challenge: high salinity can cause corrosion and limit plant growth.
Scaling – Related terms #
precipitation, mineral deposits. Scaling refers to the formation of mineral deposits, primarily calcium carbonate, on surfaces. Example: scale buildup on RO membranes reducing flux by 30 %. Practical application: antiscalant dosing before high‑pressure processes. Challenge: improper antiscalant dosage can lead to membrane fouling or excess chemical residual.
Secondary Treatment – Related terms #
biological removal, nutrient reduction. Secondary treatment employs biological processes to degrade organic matter and nutrients. Example: a trickling filter reducing BOD by 85 % and nitrates by 60 %. Practical application: improving effluent quality for reuse in landscape irrigation. Challenge: temperature sensitivity and need for careful hydraulic design.
Sedimentation – Related terms #
clarifier, settling tank. Sedimentation allows particles to settle under gravity, forming sludge at the bottom. Example: a 1‑hour residence time in a sedimentation basin achieving 70 % turbidity reduction. Practical application: a low‑cost pretreatment before filtration. Challenge: fine colloids may remain suspended, requiring subsequent coagulation.
Silica – Related terms #
SiO₂, membrane fouling. Silica is a common inorganic constituent that can precipitate and cause membrane fouling. Example: 20 mg/L silica in rainwater leading to pore blockage in RO membranes. Practical application: pre‑treatment with acid or ion exchange to reduce silica levels. Challenge: silica removal often requires specialized processes, increasing cost.
Solar Disinfection – Related terms #
SODIS, UV exposure. Solar disinfection (SODIS) uses sunlight to inactivate pathogens in clear PET bottles. Example: 6 hours of direct sunlight yielding >99 % bacterial kill. Practical application: low‑tech solution for remote households relying on harvested rainwater. Challenge: effectiveness depends on weather, water turbidity, and bottle condition.
Standard Methods – Related terms #
APHA, analytical protocols. Standard Methods are widely accepted laboratory procedures for water analysis. Example: using Standard Methods 5220 for turbidity measurement. Practical application: ensuring data comparability across labs for certification. Challenge: some methods require sophisticated equipment not available in field settings.
Surface Water – Related terms #
runoff, catchment. Surface water includes water from lakes, rivers, and runoff that can be harvested as rainwater. Example: rooftop runoff contributing 80 % of a household’s water supply. Practical application: designing catchment systems to maximize collection while minimizing contamination. Challenge: variability in quality due to atmospheric deposition and debris.
Synergistic Effects – Related terms #
combined contaminants, interaction. Synergistic effects occur when multiple contaminants together produce a greater impact than each alone. Example: low levels of chlorine and ammonia forming chloramines that are harder to remove. Practical application: comprehensive treatment design addressing multiple pollutants simultaneously. Challenge: predicting interactions requires advanced modeling and testing.
Tablet Dispenser – Related terms #
chlorine tablet, dosing unit. A tablet dispenser releases measured amounts of disinfectant tablets into water. Example: a 100‑tablet dispenser providing 0.5 mg/L chlorine over 30 days. Practical application: simple, low‑maintenance dosing for small rainwater tanks. Challenge: uneven tablet dissolution can lead to inconsistent residuals.
Temperature – Related terms #
thermal stratification, reaction kinetics. Temperature influences chemical reaction rates, microbial growth, and solubility. Example: 25 °C water improving chlorination efficiency compared with 10 °C. Practical application: selecting treatment chemicals based on expected temperature range. Challenge: extreme temperature swings in storage tanks can cause stratification and uneven treatment.
Thermal Desalination – Related terms #
multi‑effect, multi‑stage flash. Thermal desalination evaporates water and condenses the vapor, leaving salts behind. Example: a small‑scale multi‑effect unit producing 5 L/day of fresh water. Practical application: alternative to membrane processes in areas with abundant waste heat. Challenge: high energy consumption and scaling on heat exchangers.
Thiosulfate – Related terms #
dechlorinator, neutralizing agent. Thiosulfate neutralizes residual chlorine, preventing downstream damage. Example: adding 1 mg/L thiosulfate to stop chlorine before UV treatment. Practical application: protecting UV lamps and downstream ecosystems. Challenge: overdosing can lead to excess sulfite levels, requiring additional monitoring.
UV Disinfection – Related terms #
ultraviolet, germicidal. UV disinfection uses UV‑C light (254 nm) to inactivate microorganisms by damaging DNA. Example: a 30 mW UV lamp achieving 4‑log virus reduction. Practical application: chemical‑free pathogen control for potable rainwater. Challenge: UV efficacy drops with high turbidity; pre‑filtration is essential.
VOCs – Related terms #
volatile organic compounds, organic contaminants. VOCs are organic chemicals that readily vaporize, some of which may be present in rainwater from atmospheric deposition. Example: benzene concentrations of 0.2 µg/L detected in urban catchments. Practical application: activated carbon adsorption to remove VOCs before consumption. Challenge: wide variety of VOCs requires tailored sorbent selection.
Water Hardness Test – Related terms #
EDTA titration, test kit. A water hardness test determines calcium and magnesium concentrations, often using EDTA titration. Example: a field kit indicating 120 mg/L hardness in a rainwater sample. Practical application: informing softening system design. Challenge: interferences from other divalent ions may skew results.
Water Quality Index – Related terms #
WQI, composite score. The Water Quality Index aggregates multiple parameters into a single rating. Example: a WQI of 75 indicating “good” quality for irrigation. Practical application: communicating overall status to stakeholders. Challenge: weighting choices can affect interpretation; site‑specific factors must be considered.
Water Reclamation – Related terms #
reuse, tertiary treatment. Water reclamation treats wastewater to a level suitable for non‑potable or potable reuse. Example: reclaimed rainwater meeting Class C irrigation standards after advanced treatment. Practical application: augmenting municipal supply in drought‑prone regions. Challenge: public perception and regulatory approval processes.
Water Saving Devices – Related terms #
low‑flow fixtures, aerators. Water‑saving devices reduce consumption without compromising function. Example: dual‑flush toilets using 3 L for solid waste and 6 L for liquid waste. Practical application: decreasing demand on harvested rainwater storage. Challenge: ensuring user acceptance and proper maintenance.
Wetting Front – Related terms #
capillary rise, infiltration. The wetting front is the leading edge of water moving through porous media. Example: a 10 cm wetting front after 2 hours of infiltration in a sand filter. Practical application: designing filter depth to ensure complete particle capture. Challenge: heterogeneous media can cause uneven wetting, reducing efficiency.
Yield – Related terms #
capture efficiency, volume. Yield refers to the amount of water collected from a catchment over a given period. Example: a 250 L roof yielding 120 L during a storm event. Practical application: sizing storage tanks based on expected yield. Challenge: climate variability makes accurate yield prediction difficult.
Zinc Removal – Related terms #
heavy metal, ion exchange. Zinc can leach from galvanized roofing and affect water quality. Example: 0.4 mg/L zinc detected in rainwater from a metal roof. Practical application: using specific ion‑exchange resins or activated carbon to lower zinc levels. Challenge: low concentrations may still exceed drinking‑water limits, requiring sensitive monitoring.