Talk on water conservation via swimming pool removal by Mekha Pereria

1. Welcome
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Today’s Highlights:
 Industry Job Fair in the Ballroom
 Lunch at the Exhibition Hall: Awards & AZ Pure Water Brew
Challenge
 Meter Mania Finale and Top Ops Competition
 Student Poster Contest
 Awards Reception at Hyatt Regency Phoenix
AZ Water 90th Annual Conference
Thursday Morning – May 4, 2017

2. Spools, Abandonments, and Exhumations:
Have we reached peak pool?
Mekha Pereira
Mekha was an intern with Montgomery & Associates last semester
and now works with them part time.
She is an undergraduate student at the University of Arizona who is
in her final semester of a degree in Environmental Hydrology &
Water Resources and Math.

4. Pool penetration rate for new homes is ≈11%
0
2
4
6
8
10
12
14
16
2010 2011 2012 2013 2014 2015 2016 2017
SFRswithapool(%)
Construction Year
% New SFRs with Pool

5. Date of construction – pool penetration
peaked in homes built in the late 1970s
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
1939
1942
1945
1948
1951
1954
1957
1960
1963
1966
1969
1972
1975
1978
1981
1984
1987
1990
1993
1996
1999
2002
2005
2008
2011
2014
SFRswithapool(%)
Construction Year
14.9%
in ‘57
32.5%
in ‘68
36.3%
in ‘74
27.6%
in ‘94
14.1%
in ‘0911.1%
in ‘40

6. Same graph using 2009 Assessor’s data
15.5%
in ‘57
33%
in ‘68
35%
in ‘74
21%
in ‘94
6.5%
in ‘09
9.5%
in ‘40

7. Differences between 2009 and 2016 pool
penetration rates
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
1939
1942
1945
1948
1951
1954
1957
1960
1963
1966
1969
1972
1975
1978
1981
1984
1987
1990
1993
1996
1999
2002
2005
2008
2011
2014
SFRswithapool(%)
Construction Year
-0.6%
in ‘57
-0.5%
in ‘68
+1.3%
in ‘74
+6.6%
in ‘94
+7.6%
in ‘09+1.6%
in ‘40

8. Typical pools – past, present, future
Apparent trend towards smaller pools, but there are data
issues – building permit data, which contain actual pool
area and date of construction, only go back a few years.

9. Pool removal rates are approaching pool
construction rates…
… even though conservation programs aimed at
encouraging pool removals are very rare.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Maricopa Co. Chandler Gilbert Glendale Mesa Peoria Scottsdale Tempe
RatioofPoolsRemovedtoPoolsAdded

10. Scottsdale has a pool removal rebate
• began in summer 2016
• $0.50/sq ft, same as for turf removal
• the area must be re-landscaped
F Minus, Arizona Daily Star, Jan. 5, 2013

11. Three types of pool “removal”
• Quick fill – cheap, quick, but incomplete; it
leaves the decking
• Demo & fill – no visible trace of pool
remains, with pool edge & decking buried;
owner can re-landscape over where pool was
• Exhume – all traces of pool are hauled away;
owner can build on the spot where pool was,
but the most expensive approach
Really cheap option – just drain it (abandonment)

12. Pool statistics, Tucson Water service area
According to the Pima County Assessor, as of
January 2016 there are:
• 169,241 Single Family Residences in Tucson Water’s
service area
• Of these, 35,773 backyard swimming pools
• That means 21% of SFRs have a swimming pool
The County Assessor does NOT know:
• Date of pool construction
• Surface area of pools (variable is meaningless)
• When pools are removed (no building permit required)

13. Pima County pools are more skewed toward
high-end homes than in Maricopa County
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
1 2 3 4 5 6 7 8 9 10
% SFRs with Pool by Home Value Decile
Pima Maricopa

14. Home swimming pools and transition paths
New SFR
construction
SFRs with
full pool
Not nearly new
SFRs without
swimming pool
SFRs with
abandoned pool
Nearly new
SFRs without
swimming pool

18. Remote sensing shows pool status change in
4.5% of SFRs
About 1 in 22 SFRs in Tucson Water’s service
area underwent one of the following transitions
between 2008 & 2015:
• From full to removed
• From full to empty
• From full to empty to removed
• From empty to removed
Also observed and noted were transitions involving
deployment of a pool cover.

19. Pool removals by home value has a bivariate
distribution (2 peaks)
Two different motives? Save money vs. re-do back yard?
0
10
20
30
40
50
60
70
80
1 2 3 4 5 6 7 8 9 10
Numberofpoolremovals
Home value decile
Pool removal disribution by home value decile

20. While few in number, pools in lower-valued homes
are far more likely to be abandoned or removed
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
1 2 3 4 5 6 7 8 9 10
SFRsremoveapool(%)
Home value decile
% Pools removed by home value decile

21. 0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
1 2 3 4 5 6 7 8 9 10
%ofpools
Home value decile
Percent of pools abandoned vs. removed by home value decile
% pools abandoned % pools removed immediately
Pools are twice as likely to be left empty in
medium-valued homes

22. Most emptied pools are removed quickly
57% of pools are removed within 1 year; 43% are left empty
for a year or more. The average time left empty is 2.4 years.
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
20.0
1 2 3 4 5 6 7
Percentofremovedpools
Years left empty
Time between emptying and removing pool

23. Remote sensing after pools removed…
…shows virtually NO instances of pools being replaced
with turf or other high-density irrigated vegetation.

24. Engineering estimate of water
savings is problematic…
NET POOL WATER USE:
Pond evaporation rate x pool area
- Precipitation x pool area
+ Frequency of emptying & refilling x pool volume
+ Losses from pool leaks
+ Water used to backflush filters x frequency
+ Losses from pump/filter system leaks
- Pool cover usage x evaporation rate
- Irrigation of replacement land cover

25. …because all of these are uncertain
Too many unknowns and uncertainties
NET POOL WATER USE:
Pond evaporation rate x pool area
- Precipitation x pool area
+ Frequency of emptying & refilling x pool volume
+ Losses from pool leaks
+ Water used to backflush filters x frequency
+ Losses from pump/filter system leaks
- Pool cover usage x evaporation rate
- Irrigation of replacement land cover

26. Engineering estimate of water savings
NET POOL WATER USE:
77” pan evap = 62” pond evap x 500 sq ft pool
- 12” precipitation x 500 sq ft pool
+ Empty & refill every 5th year x 15,000 gals volume
+ Unknown losses from pool leaks
+ Sand filters = 400 gals x 24 backwashes
+ Unknown losses from pump/filter system leaks
- Infrequent pool cover usage in spring & fall x evap rate
- 12” x 50% land cover
= 19,323 – 3,740 + 3,000 + ??? + 9,600 + ??? - 0 - 1,870
= 26,313 gallons/year + both types of leaks

27. Alternate methodology for estimating
water demand impacts of pool removal
1. Identify pools that transition from full to empty or
removed;
2. Use remote sensing to determine periods when pool
was full, empty/gone, and unknown;
3. Get monthly billing records and days in billing period to
calculate daily residential water demand for period
encompassing all pool removals and abandonments
4. Use pooled time series – cross sectional analysis to
estimate difference in demand (delta) between full and
empty/removed pools, by month, and for each year

28. Annual distribution of demand differences
mimics monthly evaporation rates
0.00
0.20
0.40
0.60
0.80
1.00
1 2 3 4 5 6 7 8 9 10 11 12
Averagedailywateruse[ccf]
Month
Average daily water use by month for 10/2005-10/2012
Avg daily use with pool
Avg daily use without pool

29. Estimates of average annual water savings
All pools: -0.126 CCF/day = 34,401 gals/year
But a handful of pools are more than 3 standard
deviations from the mean, most on the negative
side. There are several possible explanations,
including that these pools had very large leaks.
No outliers: -0.107 CCF/day = 29,213 gals/year
Engineering estimate: 26,313 + leaks

30. Is there a trend over time?
Apparently not…
-0.25
-0.20
-0.15
-0.10
-0.05
0.00
0.05
0.10
2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015
Differenceinaveragedailywateruse
Year of Pool Removal
Delta, daily water use 1 year after vs. 1 year before pool removal
Avg delta
3yr moving average

31. Is water savings a function of home
construction date? Apparently not…
-0.50
-0.40
-0.30
-0.20
-0.10
0.00
0.10
0.20
0.30
1947 1957 1967 1977 1987 1997 2007
Delta
Year of home construction
Delta as function of home construction year
Avg delta 9yr moving average

32. Total annual costs of maintaining a pool
Cost Category Low Average High
Water and Sewer 85 105 150
Electricity 415 700 900
Liability Insurance 0 60 90
Property Taxes 0 115 200
Chemicals 400 500 700
Pool Company 0 600 1,400
Maintenance and Repairs 50 100 200
TOTAL $950 $2,180 $3,640
Average costs for unused pools may be lower than average.

33. Annual total costs of maintaining a pool
Average Costs
Water/Sewer
Electricity
Insurance
Property Taxes
Chemicals
Pool Company
Maintenance
Costs are dominated by electricity,
chemicals, and if used, a pool
service company.
Water is a much smaller expense.

34. Non-pecuniary benefits of pool removal
Other benefits include:
• Improved safety
• less risk to children and pets
• no more “attractive nuisance”
• Time freed up from maintaining the pool
• Sense of well-being from conserving water and energy
• Repurpose land
• Add landscaping, patio, etc.
• Get rid of pool fence

35. Conclusions:
We are likely at or well beyond peak pool:
• Pools are less popular now and removal rates are high in some cities
Most owners of unused pools are likely unaware of
• All the costs of maintaining a pool
• All the benefits & costs of pool removal
There is a clear opportunity for education.
Financial incentives for pool removal are problematic
because:
• The payback period is already very short.
• Many, if not most potential applicants, may have abandoned pools, and
therefore removal will not further reduce water demand.
• Most pools associated with higher-valued homes; these pool removals likely
part of re-landscaping, therefore owners may be less motivated by a rebate
There is opportunity for water savings:
• Pool water demand is estimated to be 29,213 gals/year
• When pools are removed, the area is virtually never converted to irrigated turf,
or any type of dense, irrigated landscape.

36. “Statements of fact and opinion expressed are those of
the author(s) / presenter(s).
AZ Water, AZAWWA, and AZWEA assume no
responsibility for the content, nor do they represent
official policy of the Association.”