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📐Ontario Water & Wastewater Operator Exam Reference

Formula Sheet

All the formulas you need for the OIT, Class 1–4, and WQA exams — with worked examples and exam tips. Click any formula to expand the full solution.

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CATEGORY:
💧
Flow & Volume
5 formulas
Flow Rate (Q)
Q = A × V
Units: m³/s or L/s
▼ More
Hydraulic Loading Rate (HLR)
HLR = Q ÷ A
Units: m³/m²·d or m/d
▼ More
Volume of a Cylinder
V = π × r² × h
Units: m³ or L
▼ More
Detention Time (HRT)
HRT = V ÷ Q
Units: hours or days
▼ More
Weir Overflow Rate (WOR)
WOR = Q ÷ L
Units: m³/m·d
▼ More
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Disinfection & CT
4 formulas
CT Value
CT = C × T
Units: mg·min/L
▼ More
Chlorine Dose
Dose = Demand + Residual
Units: mg/L
▼ More
Chemical Feed Rate
Feed Rate = Q × C ÷ P
Units: kg/d or L/d
▼ More
Log Inactivation
Log Inactivation = log₁₀(N₀ / N)
Units: log units
▼ More
⚗️
Chemical Dosing
4 formulas
Alum Dose (Coagulation)
Alum (kg/d) = Q (m³/d) × Dose (g/m³) ÷ 1000
Units: kg/d
▼ More
Lime Softening Dose
Lime (kg/d) = Q × [CO₂ + HCO₃ + Mg²⁺] × 0.74 ÷ 1000
Units: kg/d
▼ More
Fluoride Dose
Feed (L/d) = Q × Target ÷ (Strength × 1000)
Units: L/d
▼ More
Polymer Dose
Polymer (kg/d) = Q × Dose ÷ 1000
Units: kg/d
▼ More
⚙️
Hydraulics & Head
5 formulas
Bernoulli's Equation (Simplified)
P₁/ρg + V₁²/2g + z₁ = P₂/ρg + V₂²/2g + z₂
Units: metres of head
▼ More
Darcy-Weisbach Head Loss
hL = f × (L/D) × (V²/2g)
Units: metres of head
▼ More
Total Dynamic Head (TDH)
TDH = Static Head + Friction Losses + Minor Losses
Units: metres
▼ More
Pump Power
P = ρ × g × Q × H ÷ η
Units: Watts or kW
▼ More
Net Positive Suction Head (NPSH)
NPSHa = Ha + Hs − Hvp − Hf
Units: metres
▼ More
♻️
Wastewater Treatment
5 formulas
Sludge Volume Index (SVI)
SVI = (SV₃₀ × 1000) ÷ MLSS
Units: mL/g
▼ More
Solids Retention Time (SRT / MCRT)
SRT = (V × MLSS) ÷ (Qw × WAS + Qe × TSS_e)
Units: days
▼ More
Food-to-Microorganism Ratio (F:M)
F:M = BOD_in × Q ÷ (V × MLVSS)
Units: kg BOD / kg MLVSS · d
▼ More
BOD Removal Efficiency
E = (BOD_in − BOD_out) ÷ BOD_in × 100
Units: %
▼ More
Organic Loading Rate (OLR)
OLR = Q × BOD ÷ V
Units: kg BOD/m³·d
▼ More
📐
Math & Conversions
6 formulas
Concentration (C = m/V)
C = m ÷ V
Units: mg/L or g/m³
▼ More
Percent Solution
% = (mass of solute ÷ mass of solution) × 100
Units: %
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Unit Conversions — Flow
1 m³/s = 1,000 L/s = 86,400 m³/d = 86.4 ML/d
▼ More
Unit Conversions — Pressure
1 kPa = 0.102 m H₂O | 1 m H₂O = 9.81 kPa | 1 bar = 100 kPa
▼ More
Area of a Circle
A = π × r² = π × D² ÷ 4
Units: m²
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Specific Gravity
SG = ρ_substance ÷ ρ_water
Units: dimensionless
▼ More
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Ontario Regulations
5 formulas
O. Reg. 170/03 — Drinking Water Systems
Key Parameters: Turbidity ≤ 1 NTU (treated), Chlorine residual ≥ 0.05 mg/L, E. coli = 0 CFU/100 mL
▼ More
O. Reg. 128/04 — Certification of Drinking Water System Operators
Classes: OIT → Class 1 → Class 2 → Class 3 → Class 4 (based on system complexity)
▼ More
O. Reg. 129/04 — Certification of Wastewater System Operators
Classes: OIT → Class 1 → Class 2 → Class 3 → Class 4 (based on system complexity)
▼ More
Ontario Drinking Water Standards — Key Limits
Turbidity: ≤ 1 NTU | Chlorine: 0.05–4.0 mg/L | Fluoride: ≤ 1.5 mg/L | Nitrate: ≤ 10 mg/L | Lead: ≤ 0.01 mg/L
▼ More
Adverse Water Quality Incident (AWQI) Reporting
Report within 24 hours to: MOE Spills Action Centre (1-800-268-6060) + local Medical Officer of Health
▼ More
📌 Quick Reference — Most Common Exam Formulas
Memorize these first — they appear on almost every Ontario operator exam
CT VALUE
CT = C × T
Units: mg·min/L
CHLORINE DOSE
Dose = Demand + Residual
Units: mg/L
FLOW RATE
Q = A × V
Units: m³/s
DETENTION TIME
HRT = V ÷ Q
Units: hours
SVI
SVI = (SV₃₀ × 1000) ÷ MLSS
Units: mL/g
F:M RATIO
F:M = BOD × Q ÷ (V × MLVSS)
Units: kg/kg·d
CHEMICAL FEED
Feed = Q × Dose ÷ Purity
Units: kg/d
BOD REMOVAL
E = (BOD_in − BOD_out) ÷ BOD_in × 100
Units: %
PUMP POWER
P = ρgQH ÷ η
Units: kW
TDH
TDH = Static + Friction + Minor
Units: m