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๐Ÿ“Ontario Water & Wastewater Operator Exam Reference

Formula Sheet

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

๐Ÿ”
CATEGORY:
๐Ÿ’ง
Flow & Volume
5 formulas
Flow Rate (Q)
Q = A ร— V
Units: mยณ/s or L/s
โ–ผ More
Hydraulic Loading Rate (HLR)
HLR = Q รท A
Units: mยณ/mยฒยทd or m/d
โ–ผ More
Volume of a Cylinder
V = ฯ€ ร— rยฒ ร— h
Units: mยณ or L
โ–ผ More
Detention Time (HRT)
HRT = V รท Q
Units: hours or days
โ–ผ More
Weir Overflow Rate (WOR)
WOR = Q รท L
Units: mยณ/mยทd
โ–ผ More
๐Ÿงช
Disinfection & CT
4 formulas
CT Value
CT = C ร— T
Units: mgยทmin/L
โ–ผ More
Chlorine Dose
Dose = Demand + Residual
Units: mg/L
โ–ผ More
Chemical Feed Rate
Feed Rate = Q ร— C รท P
Units: kg/d or L/d
โ–ผ More
Log Inactivation
Log Inactivation = logโ‚โ‚€(Nโ‚€ / N)
Units: log units
โ–ผ More
โš—๏ธ
Chemical Dosing
4 formulas
Alum Dose (Coagulation)
Alum (kg/d) = Q (mยณ/d) ร— Dose (g/mยณ) รท 1000
Units: kg/d
โ–ผ More
Lime Softening Dose
Lime (kg/d) = Q ร— [COโ‚‚ + HCOโ‚ƒ + Mgยฒโบ] ร— 0.74 รท 1000
Units: kg/d
โ–ผ More
Fluoride Dose
Feed (L/d) = Q ร— Target รท (Strength ร— 1000)
Units: L/d
โ–ผ More
Polymer Dose
Polymer (kg/d) = Q ร— Dose รท 1000
Units: kg/d
โ–ผ More
โš™๏ธ
Hydraulics & Head
5 formulas
Bernoulli's Equation (Simplified)
Pโ‚/ฯg + Vโ‚ยฒ/2g + zโ‚ = Pโ‚‚/ฯg + Vโ‚‚ยฒ/2g + zโ‚‚
Units: metres of head
โ–ผ More
Darcy-Weisbach Head Loss
hL = f ร— (L/D) ร— (Vยฒ/2g)
Units: metres of head
โ–ผ More
Total Dynamic Head (TDH)
TDH = Static Head + Friction Losses + Minor Losses
Units: metres
โ–ผ More
Pump Power
P = ฯ ร— g ร— Q ร— H รท ฮท
Units: Watts or kW
โ–ผ More
Net Positive Suction Head (NPSH)
NPSHa = Ha + Hs โˆ’ Hvp โˆ’ Hf
Units: metres
โ–ผ More
โ™ป๏ธ
Wastewater Treatment
5 formulas
Sludge Volume Index (SVI)
SVI = (SVโ‚ƒโ‚€ ร— 1000) รท MLSS
Units: mL/g
โ–ผ More
Solids Retention Time (SRT / MCRT)
SRT = (V ร— MLSS) รท (Qw ร— WAS + Qe ร— TSS_e)
Units: days
โ–ผ More
Food-to-Microorganism Ratio (F:M)
F:M = BOD_in ร— Q รท (V ร— MLVSS)
Units: kg BOD / kg MLVSS ยท d
โ–ผ More
BOD Removal Efficiency
E = (BOD_in โˆ’ BOD_out) รท BOD_in ร— 100
Units: %
โ–ผ More
Organic Loading Rate (OLR)
OLR = Q ร— BOD รท V
Units: kg BOD/mยณยทd
โ–ผ More
๐Ÿ“
Math & Conversions
6 formulas
Concentration (C = m/V)
C = m รท V
Units: mg/L or g/mยณ
โ–ผ More
Percent Solution
% = (mass of solute รท mass of solution) ร— 100
Units: %
โ–ผ More
Unit Conversions โ€” Flow
1 mยณ/s = 1,000 L/s = 86,400 mยณ/d = 86.4 ML/d
โ–ผ More
Unit Conversions โ€” Pressure
1 kPa = 0.102 m Hโ‚‚O | 1 m Hโ‚‚O = 9.81 kPa | 1 bar = 100 kPa
โ–ผ More
Area of a Circle
A = ฯ€ ร— rยฒ = ฯ€ ร— Dยฒ รท 4
Units: mยฒ
โ–ผ More
Specific Gravity
SG = ฯ_substance รท ฯ_water
Units: dimensionless
โ–ผ More
๐Ÿ“‹
Ontario Regulations
5 formulas
O. Reg. 170/03 โ€” Drinking Water Systems
Key Parameters: Turbidity โ‰ค 1 NTU (treated), Chlorine residual โ‰ฅ 0.05 mg/L, E. coli = 0 CFU/100 mL
โ–ผ More
O. Reg. 128/04 โ€” Certification of Drinking Water System Operators
Classes: OIT โ†’ Class 1 โ†’ Class 2 โ†’ Class 3 โ†’ Class 4 (based on system complexity)
โ–ผ More
O. Reg. 129/04 โ€” Certification of Wastewater System Operators
Classes: OIT โ†’ Class 1 โ†’ Class 2 โ†’ Class 3 โ†’ Class 4 (based on system complexity)
โ–ผ More
Ontario Drinking Water Standards โ€” Key Limits
Turbidity: โ‰ค 1 NTU | Chlorine: 0.05โ€“4.0 mg/L | Fluoride: โ‰ค 1.5 mg/L | Nitrate: โ‰ค 10 mg/L | Lead: โ‰ค 0.01 mg/L
โ–ผ 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
โ–ผ More
๐Ÿ“Œ Quick Reference โ€” Most Common Exam Formulas
Memorize these first โ€” they appear on almost every Ontario operator exam
CT VALUE
CT = C ร— T
Units: mgยทmin/L
CHLORINE DOSE
Dose = Demand + Residual
Units: mg/L
FLOW RATE
Q = A ร— V
Units: mยณ/s
DETENTION TIME
HRT = V รท Q
Units: hours
SVI
SVI = (SVโ‚ƒโ‚€ ร— 1000) รท MLSS
Units: mL/g
F:M RATIO
F:M = BOD ร— Q รท (V ร— MLVSS)
Units: kg/kgยทd
CHEMICAL FEED
Feed = Q ร— Dose รท Purity
Units: kg/d
BOD REMOVAL
E = (BOD_in โˆ’ BOD_out) รท BOD_in ร— 100
Units: %
PUMP POWER
P = ฯgQH รท ฮท
Units: kW
TDH
TDH = Static + Friction + Minor
Units: m