Just use the water meters already!

There was an article in The Herald recently about the RDOS's failure to use the West Bench's newly installed water meters for billing.  Fair enough, but please appreciate that the goal here is not to drag our heels but rather save some people unnecessary anxiety.

As readers of this blog might know, I have been taking a look at the water meter data as it becomes available every month (e.g., see this posting from August 2015).  The issue we have is huge variability in recorded water usage among some residential properties.  This variance could be caused by:

  1. Extreme water use (customer's fault)
  2. Leaks (RDOS's fault/problem)
  3. Meter reading errors (RDOS's fault/problem)


What does this variance mean? Let's put it in terms of dollars.  Assume we go with the simplest possible metered price and charge everyone $0.25 per cubic meter of water (what we pay the City of Penticton).  [Aside: Our variable costs are higher, of course, because the bulk price we pay to Penticton does not include the cost of pumping it up the hill.  But let's keep it simple for now.]

A useful tool for visualizing the distribution of monthly readings is the box plot.  You may be unfamiliar with box plots (most people are) so here is a quick guide stolen from this site:

The important thing to know about box plots is that we should expect 50% of observed values to fall within the box and all observed values to fall within the maximum and minimum "whiskers".  Everything else is an outlier--a statistically weird outcome.

Here is the data for the West Bench by month.  Notice that the monthly cost (if we billed at $0.25/m3) is on the vertical axis and month number (1=January, 2=February...) is on the horizontal axis.

As always, consumption (and thus cost) increases in the summer months as folks water their lawns.  But I am more concerned with the dots on the high end of the box plots.  These are the outliers.  And if you take an outlier and read the monthly cost off the vertical axis, you will see that we are talking about some pretty big numbers here.  The most obvious outlier (top right) corresponds to a cost of about $900/month.  These dots are not farms--these are residential properties.  I have a hard time believing that someone used $900 of water in a month.

But even if we throw out the extreme outlier, we still see some very high meter readings.  For example, the median usage in July is around $50 for the month while the maximum usage is closer to $340.  This is for one month.  We need to understand more about the root causes of these differences before we start sending out massive water bills to some and tiny water bills to others.



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