The Software Engineer role at Culligan International is pivotal to the company's mission of delivering innovative water treatment solutions globally. As a Software Engineer, you will be responsible for designing, developing, and maintaining software applications that enhance our product offerings and improve user experiences. This role not only impacts the functionality of our systems but also directly contributes to customer satisfaction and operational efficiency. Your work will support teams that develop smart water solutions, ensuring that our products meet the evolving needs of consumers and businesses alike. At Culligan International, you will encounter complex challenges that require both technical expertise and creative problem-solving. You will collaborate with cross-functional teams, including product management and operations, to drive projects from conception through deployment. The diversity of projects you will engage with—from application development to integration with IoT devices—makes this position both critical and rewarding. Expect a dynamic work environment where your contributions will have a tangible impact on the business and its customers.
Phone Screen
reportedInitial call to assess candidates' fit for the Software Engineer position.
What to demonstrate
- Initial call to assess candidates' fit for the Software Engineer position
- Depth in Recruiting and Candidate Communication
How to prepare
- Be able to walk your CV end to end in two minutes, and say why this company specifically.
- Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.
In-Person/Virtual Interviews
reportedOne or more interviews with technical leads and team members to evaluate technical skills and cultural fit.
What to demonstrate
- One or more interviews with technical leads and team members to evaluate technical skills and cultural fit
- Depth in Recruiting and Candidate Communication
How to prepare
- Answer aloud and timed: Describe a challenging technical problem you solved and the approach you took.
- Answer aloud and timed: How do you ensure code quality and maintainability in your projects?
PracHub editorial advice for the preparation topics above.
Practice coding problems
Use platforms like LeetCode or HackerRank to sharpen your coding skills and problem-solving abilities.
Prepare for behavioral questions
Use the STAR method (Situation, Task, Action, Result) to structure your responses effectively.
Research the company
Familiarize yourself with Culligan International's mission, values, and recent initiatives to demonstrate your interest during the interview.
Network with current employees
If possible, connect with current or former employees to gain insights into the company culture and interview process.
Choose a category, try a prompt, then open its approach, worked solution or follow-up when you need it.
Write a function to reverse a string.
Write a function to reverse a string.
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
Explain the difference between a stack and a queue, and provide use cases for each.
Explain the difference between a stack and a queue, and provide use cases for each.
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
How would you find the longest substring without repeating characters?
How would you find the longest substring without repeating characters?
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
Can you implement a binary search algorithm?
Can you implement a binary search algorithm?
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
Discuss the time and space complexities of different sorting algorithms.
Discuss the time and space complexities of different sorting algorithms.
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
Stop tag and share joins from fanning out a page
resource_tag is (resource_id, tag_id) with PK (resource_id, tag_id); resource_share is (resource_id, shared_with_user_id, permission). The tagged-and-shared listing inner-joins resource to both, filters tenant_id, tag_id = ANY($2) and shared_with_user_id = $3, orders by updated_at DESC and takes 50. Pages come back with fewer than 50 distinct resources and the total in the header is far too high. Explain the row multiplication, rewrite both the page query and the count query so each is correct, and name the index each one needs. PostgreSQL 16.
Approach
- Do the arithmetic against the predicates that are actually there. An inner join emits one row per matching child row, and both joins are filtered: tag_id = ANY($2) admits only the requested tags, shared_with_user_id = $3 admits one user's share rows. So a resource holding three of the requested tags and shared with $3 once yields three rows, not one — the multiplier is its count of matching tags times its share rows for that single user, and that second factor is 1 unless the table admits duplicate (resource_id, shared_with_user_id) pairs. LIMIT 50 then limits rows rather than resources, and COUNT(*) counts pairs — the header is the product, not the population.
- Reject DISTINCT as the fix. It deduplicates after the product has been built, so the planner must materialise and sort the fanned-out set before the LIMIT can apply, and it leaves any SUM or AVG in the same select list wrong.
- Rewrite both filters as semi-joins, keeping resource as the only row source: AND EXISTS (SELECT 1 FROM resource_tag rt WHERE rt.resource_id = r.resource_id AND rt.tag_id = ANY($2)) and the same shape against resource_share. A semi-join stops at the first match per resource and preserves the driving index order, so ORDER BY updated_at DESC, resource_id DESC LIMIT 50 still stops after 50 rows.
- Count with the same predicates and no join at all: SELECT count(*) FROM resource r WHERE r.tenant_id = $1 AND r.status = 'active' AND EXISTS (...) AND EXISTS (...). Nothing multiplies a resource, so the number is the population.
Follow-up
- The filter changes from 'any of these tags' to 'all of these tags'. Rewrite it and state what it costs relative to the ANY form.
- A resource can be shared with the same user twice under different permissions. Does your count change, and should it?
Write the update path that detects a concurrent edit
resource carries version INT NOT NULL DEFAULT 1. resource_revision holds revision_id, resource_id, version, actor_user_id, change_kind, patch JSONB, request_id, created_at with UNIQUE (resource_id, version). outbox_event holds aggregate_type, aggregate_id, aggregate_version, event_type, payload, status. A PUT carries the version the client read. Write the exact statements for the single transaction that applies the edit, records the revision and enqueues 'resource.updated', and give the handler's branch on zero affected rows. Then say what PostgreSQL 16 does under READ COMMITTED when two of these updates hit one row at once.
Approach
- One transaction, three writes, no network call inside it: UPDATE resource SET title = $3, version = version + 1, updated_at = now() WHERE resource_id = $1 AND tenant_id = $4 AND version = $2; then INSERT the resource_revision row at version $2 + 1; then INSERT the outbox_event row at the same aggregate_version. The event goes to a table rather than a broker because no transaction spans both.
- Branch on the affected-row count before doing anything else. Zero has three causes — stale version, wrong tenant, row gone — so re-read once and map to 409 carrying the current version, or 404 for an id outside the caller's tenant, which also stops the endpoint confirming that another tenant's id exists.
- State the engine behaviour instead of assuming it. Under READ COMMITTED the second UPDATE blocks on the row lock, and when the first commits PostgreSQL re-evaluates the WHERE clause against the newly committed row, so the version predicate now fails and the statement reports zero rows. Under REPEATABLE READ the identical collision raises SQLSTATE 40001 instead, so the handler must fold both shapes into one conflict response.
- Keep UNIQUE (resource_id, version) even though the predicate already serialises writers. It is what makes a lost update unwritable if any other path ever reaches the revision table, and it converts a logic bug into 23505 rather than into a silently missing history row.
Follow-up
- A client sends the version it read ten minutes ago and the resource has moved three versions. What is in your 409 so it can resolve the conflict without a full re-fetch?
- Two editors, two disjoint fields, no overlap. Does your answer still refuse the second write, and should it?
What programming languages are you proficient in, and how have you applied them?
What programming languages are you proficient in, and how have you applied them?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
Describe a challenging technical problem you solved and the approach you took.
Describe a challenging technical problem you solved and the approach you took.
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
How do you ensure code quality and maintainability in your projects?
How do you ensure code quality and maintainability in your projects?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
How would you approach designing a new application from scratch?
How would you approach designing a new application from scratch?
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- State the consistency you need, and where you are willing to be stale.
Follow-up
- What breaks first when traffic grows ten times?
- How does this behave when that dependency is down for an hour?
Discuss the trade-offs between different architectural patterns.
Discuss the trade-offs between different architectural patterns.
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- State the consistency you need, and where you are willing to be stale.
Follow-up
- What breaks first when traffic grows ten times?
- How does this behave when that dependency is down for an hour?
Describe how you would scale a system to handle increased user demand.
Describe how you would scale a system to handle increased user demand.
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- State the consistency you need, and where you are willing to be stale.
Follow-up
- What breaks first when traffic grows ten times?
- How does this behave when that dependency is down for an hour?
What considerations do you take into account when designing APIs?
What considerations do you take into account when designing APIs?
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- State the consistency you need, and where you are willing to be stale.
Follow-up
- What breaks first when traffic grows ten times?
- How does this behave when that dependency is down for an hour?
Can you provide an example of a system you designed and the challenges you faced?
Can you provide an example of a system you designed and the challenges you faced?
Approach
- Fix the scope first: who calls this, how often, and what they do when it fails.
- Name the read and write paths separately; they rarely have the same bottleneck.
- Choose a partition key and say what query it makes expensive.
- State the consistency you need, and where you are willing to be stale.
Follow-up
- What breaks first when traffic grows ten times?
- How does this behave when that dependency is down for an hour?
Walk us through your thought process for solving a complex problem.
Walk us through your thought process for solving a complex problem.
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
What is your process for evaluating different solutions to a problem?
What is your process for evaluating different solutions to a problem?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
Describe a project where you had to pivot due to unforeseen challenges.
Describe a project where you had to pivot due to unforeseen challenges.
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
How do you approach debugging a difficult issue in a codebase?
How do you approach debugging a difficult issue in a codebase?
Approach
- Establish what changed and when, before forming any theory.
- Pick a bisection that eliminates candidates whichever way it turns out.
- Check the instrumentation before believing the symptom.
- Separate the trigger from the cause; the deploy is rarely the bug.
Follow-up
- What would you look at first, and what would it rule out?
- How would you tell a cause from a coincidence here?
Built from the rounds and topics Culligan International candidates report.
Prepare, practise & reflect
One practical outcome each day. Spend longer where you need it.
0 / 7 done01Map the Culligan International loop
- Write out the reported sequence: Phone Screen, In-Person/Virtual Interviews.
- For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.
Deliverable: A one-page map of the 2 reported rounds, with the weakest marked.
02Work Recruiting and Candidate Communication
- Spend the session on Recruiting and Candidate Communication, which Culligan International candidates report being tested on.
- Write one worked example in Recruiting and Candidate Communication and time yourself on it.
Deliverable: One timed worked example in Recruiting and Candidate Communication.
03Work Interview Process Coordination
- Spend the session on Interview Process Coordination, which Culligan International candidates report being tested on.
- Write one worked example in Interview Process Coordination and time yourself on it.
Deliverable: One timed worked example in Interview Process Coordination.
04Work Preparation for Interview Rounds
- Spend the session on Preparation for Interview Rounds, which Culligan International candidates report being tested on.
- Write one worked example in Preparation for Interview Rounds and time yourself on it.
Deliverable: One timed worked example in Preparation for Interview Rounds.
05Answer out loud: Technical / Domain Questions
- Answer aloud, timed: Explain the software development lifecycle and your experience with it.
- Answer aloud, timed: What programming languages are you proficient in, and how have you applied them?
Deliverable: Spoken answers to 2 reported Technical / Domain Questions question(s), under time.
06Answer out loud: Behavioral / Leadership
- Answer aloud, timed: Describe a time when you had to work in a team to achieve a common goal.
- Answer aloud, timed: How do you handle conflict with a colleague or team member?
Deliverable: Spoken answers to 2 reported Behavioral / Leadership question(s), under time.
07Answer out loud: System Design / Architecture
- Answer aloud, timed: How would you approach designing a new application from scratch?
- Answer aloud, timed: Discuss the trade-offs between different architectural patterns.
Deliverable: Spoken answers to 2 reported System Design / Architecture question(s), under time.
Expand any day for tasks and deliverables. Your progress is saved on this device.
Behavioural rounds judge the decision you made and what it cost.
Explain the software development lifecycle and your experience with it.
Explain the software development lifecycle and your experience with it.
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
Discuss your experience with database management and optimization.
Discuss your experience with database management and optimization.
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
Describe a time when you had to work in a team to achieve a common goal.
Describe a time when you had to work in a team to achieve a common goal.
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
How do you handle conflict with a colleague or team member?
How do you handle conflict with a colleague or team member?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
Can you provide an example of how you have taken initiative in a project?
Can you provide an example of how you have taken initiative in a project?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
What motivates you to stay engaged and productive in your work?
What motivates you to stay engaged and productive in your work?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
How do you prioritize tasks in a fast-paced environment?
How do you prioritize tasks in a fast-paced environment?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
Provide an example of a time when you had to adapt your solution based on new information.
Provide an example of a time when you had to adapt your solution based on new information.
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
- 01
Explain the software development lifecycle and your experience with it.
- 02
Discuss your experience with database management and optimization.
- 03
Describe a time when you had to work in a team to achieve a common goal.
- 04
How do you handle conflict with a colleague or team member?
How difficult are the interviews at Culligan International?
The interviews are generally considered to be of average difficulty. Candidates should prepare for a balanced mix of technical and behavioral questions.
Culligan International Software Engineer candidate reports ↗What differentiates successful candidates?
Successful candidates typically demonstrate a strong technical foundation, effective communication skills, and a genuine alignment with the company's values.
Culligan International Software Engineer candidate reports ↗What is the culture like at Culligan International?
The culture is collaborative and supportive, with a focus on innovation and continuous improvement. Employees are encouraged to share ideas and contribute to the company's success.
Culligan International Software Engineer candidate reports ↗What is the typical timeline from initial screen to offer?
The entire interview process can take anywhere from a few weeks to a couple of months, depending on the number of candidates and scheduling.
Culligan International Software Engineer candidate reports ↗Are there remote work options?
Culligan International offers flexible work arrangements, including remote work options. However, candidates should confirm specifics during the interview process.
Culligan International Software Engineer candidate reports ↗How much preparation time is typical?
Candidates typically spend 2-4 weeks preparing for interviews, focusing on both technical skills and behavioral questions.
Culligan International Software Engineer candidate reports ↗What topics does Culligan International test in interviews?
Culligan International interviews most often cover Data Analysis, Interview Question Handling, Marketing Analytics, Financial analysis, and Sales Background & Experience. The exact emphasis depends on the specific role you apply for.
Culligan International Software Engineer candidate reports ↗Sources & methodology 3 sources ↗
No official company page is cited. Rounds and questions come from candidate reports and PracHub editorial material; each source shows the date it was read.
- 01Culligan International Software Engineer candidate reports ↗
Company-reported rounds, questions and FAQ.
Candidate reports · Accessed 2026-09-22 - 02PracHub Software Engineer practice ↗
PracHub practice material, not company-reported.
PracHub page · Accessed 2026-09-22 - 03PracHub preparation framework ↗
PracHub preparation guidance.
PracHub page · Accessed 2026-09-22
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