CWS Study Guide 2026
Everything you need to pass the CWS exam in one place: the exam format, every topic to study, real practice questions with explanations, flashcards, and full-length practice tests. Free, no sign-up needed.
📋 CWS Exam Format at a Glance
📚 CWS Topics to Study (69)
✍️ Sample CWS Questions & Answers
1. An acid neutralizer using calcite media is sized for a 10 gpm service flow. To prevent calcite loss during backwash, what maximum backwash rate is typically specified?
Calcite backwash rates are typically kept at or below 5 gpm/ft² to achieve bed expansion without washing calcite particles out of the tank.
2. What is a common pitfall when implementing ultraviolet disinfection systems practices?
A common pitfall is either rigidly following templates without adaptation or ignoring core principles entirely, rather than finding the right balance.
3. Which characteristic is described by the 'uniformity coefficient' (UC) of a filter media?
The uniformity coefficient is d60/d10, where d60 is the sieve size passing 60% of the media and d10 is the effective size; a lower UC indicates a more uniform particle distribution.
4. Which of the following contaminants is BEST addressed by a POE system rather than a POU system?
Hydrogen sulfide that affects all fixtures—including showers where inhalation is a concern—warrants a whole-house POE treatment solution.
5. Which water quality parameter, if elevated, most reduces UV system effectiveness by absorbing UV light before it reaches pathogens?
Dissolved organic carbon, tannins, and color compounds absorb UV at 254 nm, lowering UVT and reducing germicidal dose delivered to microorganisms.
6. Which regulatory document provides the primary US guidance for UV disinfection of drinking water at large surface water systems?
The USEPA UVDGM (2006) provides comprehensive guidance on reactor validation, dose monitoring, and operational requirements for compliance under the LT2ESWTR.