By Bob Young

As a retired statistician, I become very curious when I see a lot of numbers being floated around that are in conflict. I am often reminded about the book, “How to Lie with Statistics.” Most statisticians abhor that concept.

The purpose of this note is to provide some understanding (for me) as to the costs of our new city of Davis water program. I have computed costs for our single residence two ways: first, by using 41 hundred cubic feet (ccf) that we use every two months, for this year, for 2012 and for 2016, and second, using the levels specified by maximum Tier 1 amounts, that is, 36 ccf this year, 27 ccf next year and 23 ccf in 2016.

I do make a large assumption that we can reduce to Tier 1 levels through increased conservation. When we get safe and reliable drinking water delivered through our system, I will not treat this water in the same way as I treat our ground water. The “new” water will be more valuable and will be more appreciated. Conservation will happen.

My goal is reduce consumption to the levels specified in Tier 1 for 2012 through 2016, namely, 27 ccf next year and 23 ccf in 2016.

Now, for the numbers.

Assumption 1: using 41 ccf for all three computations; 2011 (current) combined, $86.50 (base = $23, tier 1 = $54 (36 ccf @ $1.50), and tier 2 = $9.50 (5 ccf @ 1.90)), 2012 combined, $115.34 (base = $29.60, tier 1 = $51.30 (27 ccf @ 1.90), tier 2 = $34.44 (14 ccf @ $2.46)); 2016 combined, $227.52 (base = $61.20, tier 1 = $82.80 (23 ccf @ $3.60), tier 2 = $83.52 (18 ccf @ $4.64)).

I am showing the calculations in a set of five numbers, (year, ccf used in calculations, costs, year-over-year percent change and monthly increase): (2011, 41, $86.50, na, na), (2012, 41, $115.34, 33, $14.42), (2013, 41, $143.39, 24, $14.02), (2014, 41, $171.44, 20, $14.02), (2015, 41, $199.49, 16, $14.02), (2016, 41, $227.52, 14, $14.02).

When averaging the year-over-year percentage increases — 33, 24, 20, 16 and 14 percent — the combined average change is 21.4 percent. The resultant monthly change is around $14. I hope the city will consider billing us monthly in the future.

Assumption 2: using tier 1 consumptions to compute current bill and future, using 36 ccf, 27 ccf and 23 ccf, respectively: 2011 (current) combined, $77 (base = $23, tier 1 = $54 (36 ccf @ $1.50)); 2012 combined, $80.90 (base = $29.60, tier 1 = $51.30 (27 ccf @ $1.90)); 2016 combined, $144 (base = $61.20, tier 1 = $82.80 ( 23 ccf @ $3.60)).

I am showing the calculations in a set of five numbers, (year, ccf used in calculations, costs, year-over-year percent change and monthly increase): (2011, 36, $77, na, na), (2012, 27, $80.90, 5, $1.95), (2013, 26, $96.68, 20, $7.89), (2014, 25, $112.46, 16, $7.89), (2015, 24, $128.24, 14, $7.89), (2016, 23, $144, 12, $7.88).

When averaging the year-over-year percentage increases — 5, 20, 16, 14 and 12 percent — the combined average change is 13.4 percent! The resultant monthly change is about $8.

I would support the argument that for those households that use around 25 ccf, the percentage change would be around 14 percent. And for those households that continue to use around 41 ccf, the percentage change would be around 21 percent.

I suggest that everyone do this exercise and determine their own percentage change. Numbers used for my calculations follow: “base” charges per cycle (two months) are $23 for 2011, $29.60 for 2012, and $61.20 for 2016; tier 1 charges are $1.50 per hundred cubic feet (ccf) for first 36 ccf in 2011, $1.90 per ccf for first 27 ccf in 2012 and $3.60 per ccf for first 23 ccf in 2016; tier 2 charges are $1.90 per ccf for over 36 ccf in 2011, $2.46 per ccf for over 27 ccf in 2012 and $4.64 per ccf for over 23 ccf in 2016.

I had to call the city to get the “base” amounts. All other numbers are on the city’s website.

Let the calculators start.

— Bob Young is a Davis resident.

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