Apply water balance to determine size and performance of a rainwater harvesting system
Part 1. Sizing Cistern Using Monthly Water Balance (10 min)
For this part of the exercise, students will insert into a spreadsheet or worksheet the values for water yield and water demand to identify the size of cistern needed to store the surplus water for use in times of need.
Insert runoff values from Unit 5 Net Zero Check spreadsheet into the Yield column of the Unit 6 Cistern Sizing Spreadsheet.
Insert demand values from Unit 5 Net Zero Check spreadsheet and insert into the Demand column of Unit 6 Cistern Sizing Spreadsheet.
Identify the maximum cumulative storage value. This represents the approximate size of the cistern to fully capture the surplus water.
Consider the size specified. Use your judgment to evaluate its appropriateness in terms of size and estimated cost.
Be prepared to report to class (a) size (in gallons) of cistern and (b) judgment of reasonableness. Reasonableness is based on many factors, but a few to consider include the size of cistern relative to available space, policy and laws, need for significant remodel of indoor plumbing, cost.
Part 2. Sizing Cistern for Different Demand Patterns (20 min)
Student teams explore different demand patterns representing (1) outdoor demand only and (2) indoor non-potable demand only.
For option 1, modify the demand values in the Unit 6 spreadsheet by only including the outdoor demand values from Unit 4 or 5. Record size of cistern.
For option 2, identify non-potable demands from Unit 5 and insert into Unit 6 spreadsheet. Record size of cistern.
Be prepared to report to class (a) size of cistern and (b) whether rainwater harvesting is better for indoor or outdoor water demand provision for this case study.
Part 3. Individual Report and Discussion (10 min)
Individuals work on their deliverables for the activity: (1) completed spreadsheets/worksheets, (2) one paragraph summary of activity with results stated, and (3) answers to discussion question: Is rainwater harvesting a sustainable practice in the case study location?