How important is water conservation and how can it be increased?
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This section, along with Table 1 , summarizes the water savings hypothesis and evaluation design for each of the four demonstration projects. The WSICS are designed to only trigger an irrigation cycle when the soil moisture is low, as estimated from regional weather conditions and local rainfall.
By delivering water optimally, such technology should reduce overall irrigation demand by eliminating extraneous cycles triggered by automatic timers that are insensitive to weather conditions. The rainwater harvesting systems store rainwater, providing a direct alternative to the use of public drinking water for nonpotable outdoor uses.
Saving Water, Saving Money and Saving the Earth – Water Conservation Guide
We thereby anticipated that the systems would reduce demand on household public water consumption. The moisture-retaining soil amendments were designed to extend the time that moisture remains available to the turf roots within the soil. As a result, we anticipated that the field could tolerate reductions in irrigation volume without compromising turf health.
The rebate program was anticipated to similarly reduce household water use by encouraging the conversion to water-efficient toilets and washing machines. A summary of evaluation design for all four water conservation strategies is documented in Table 1. This table includes the sample sizes associated with the control and experimental populations, the time periods associated with the installation and the pre- and postexperiment evaluations, the time periods excluded from the analysis, and a list of the confounding factors.
We used nonparametric confidence intervals for the true population median because the probability distributions of the original random variables could not be confirmed for small samples. Such confidence intervals for the true population median, shown in many subsequent figures, are used to assess whether the median estimated from one sample differs from the median estimated from another sample. Helsel and Hirsch suggested that the nonparametric interval for the median can be estimated using the binomial probability distribution.
For a sample size n , the cumulative probability p x of x observations exceeding the median is then. The resulting confidence intervals for the median reflect the distributions of the estimates of medians drawn from any dataset of length n. In some instances, we were able to employ hypothesis tests based on the assumption of a normal distribution. To check whether observations of a sample are normally distributed, the normal probability plot correlation coefficient PPCC was computed and checked against its critical value given in table The normal quantiles were estimated using Blom's unbiased, plotting position for normal variates Stedinger et al.
The hypothesis tests used in this study, corresponding to the various types of comparisons, are documented in Table 2.
The sign test was chosen over the sign rank test and the paired rank-sum test because the latter two assume a symmetrical distribution of the observations and most of our datasets are asymmetrical. The following sections summarize the effectiveness at reducing water demand of the four water conservation strategies. Based on this information, the WSICS device is designed to deliver water only when needed by the landscape. Approximately residences in the town of Reading, MA, have exclusive outdoor water meters. Among this group, nine households that met our experimental group criteria had WSICS installed during the summer of , and two during the following two summers.
Criteria included continuous ownership and use of an automatic irrigation system since An additional 71 households with dedicated outdoor meters meeting these criteria were selected as the control group. For this analysis, quarterly outdoor water use records were obtained from the Reading Water Department for all households in the study from January through November Data from were excluded from the analysis due to this being a transitional year.
Because a PPCC normality test determined that the control group was not well approximated by a normal distribution, the nonparametric rank-sum hypothesis test was used to compare the water use of both the control and experimental groups as shown in Figure 1. However, a visual assessment of Figure 1 also suggests that the WSICS may have reduced the variability of water use among the experimental group, especially among high water users.
The results of a rank-sum test do not show that the water savings for households with the WSICS were different than for the control group. The large range associated with the confidence interval Figure 2 for the median of the experimental group is due to the small experimental sample size and large variation in response to the WSICS installation within the group. Nevertheless, Figure 2 illustrates that although the average household in the control group saw a drop in water demand of 3.
These results suggest that households with high irrigation water demands are more likely to reduce their water use due to the WSICS installations. Our analysis also highlights the importance of increasing the sample size of the experimental group of households in any future studies. A retrospective analysis of the WSICS compared actual outdoor water used by each experimental household in and to the estimated volume of water that would have been applied by the WSICS during that same period.
The number of triggered irrigation cycles was then converted to a volume for each household by multiplying it by the appropriate per-cycle volume.
The latter was determined at each residence by reading the water meter before and after a test irrigation cycle. This approach was only applied to and to coincide with the years for which the extensive weather data needed in the algorithm was available. A PPCC normality hypothesis test suggests that the nonparametric sign test is preferred over a parametric test for assessing the difference between the actual and simulated water uses.
Although positive overall mean and median water savings However, this sample consisted only of one year of data for each of three households. In summary, two approaches were used: 1 comparing outdoor water use in households where WSICS were installed to outdoor water use in control households, both prior to and after installation; and 2 the retrospective analysis, comparing actual water use to theoretical water use had the WSICS been installed in and Both approaches confirm that even though overall water savings for the experimental group is greater than that for the control group, the difference in the savings between the two groups was not statistically significant owing to the highly variable savings in the experimental group.
WSICS were, however, likely to result in water savings when installed at residences with high outdoor water demands. Although we did not assess the efficiency of individual watering regimes prior to WSICS installation, the significant response to the systems among the highest water users suggests over-watering by these households prior to the WSICS installation, as WSICS systems are designed specifically to reduce unnecessary irrigation.
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A retrospective analysis was conducted using the same methodology as described above for the residential participants. Hypothetical water use was derived by simulating irrigation triggers that would have been signaled by the WSICS, had they been installed during and , using weather records from that period and each field's WSICS ET thresholds and irrigation cycle volumes. This simulated use was compared with actual water use for each of the five fields aggregated for and Figure 4. Theoretical water savings were obtained by subtracting simulated use from actual use for each field for each year.
Nonparametric tests were used again due to a sample size of 10 two years each, for five fields. The sign test indicates that a significant positive water savings would have resulted from the WSICS installations. A box plot of the theoretical water savings Figure 5 indicates that this statistically significant average savings was approximately 0. Mean per-unit-area savings is 0.
Rainwater harvesting systems are designed to capture runoff from rooftops and store the water for nonpotable uses, such as lawn and garden watering.
Guide How important is water conservation and how can it be increased?
One intent of such systems is to reduce demand on public water supplies by replacing potable water that would otherwise be used for these outdoor purposes. A total of 39 rainwater harvesting systems were installed on residential properties mid-April in the town of Wilmington, MA, based on a lottery among interested households. The systems consist of a storage tank, a pressure pump to aid in water distribution, a spigot for a hose, and a water meter to measure flow pumped from the tanks. Two different sizes of storage tanks were installed: twenty-eight 0.
Two of the participants with gallon tanks upgraded their storage capacity to 1. Except where otherwise noted, the households with upgraded systems were excluded from the analyses. The rainwater systems were in use during the summers of and Total rainwater use from the time each system was turned on in the spring to when it was decommissioned in the fall was recorded for each household for and The distribution of the rainwater use observations for both groups is well-approximated by a normal distribution. All households used the rainwater systems, and a two-sample Student's t hypothesis test on sample means indicates that those with 3.
To assess whether the use of rainwater resulted in a decrease in domestic water use, domestic water use before and after the installation of the rainwater harvesting system was compared for each residential participant. The visual comparison of the domestic water use and the rainwater use in Figure 7 shows that the volumes of rainwater used were generally less than the fluctuation in domestic water use from year to year, making reductions in domestic water use due to rainwater difficult to discern. A rank-sum test confirmed that, regardless of the size of the tanks, rainwater systems could not be shown to impact summer domestic water use.
However, a written survey completed by all participants who attended a meeting at the conclusion of the study suggests qualitatively that rainwater was a frequent substitute for domestic water among the rainwater harvesting participants. All respondents 19 of 37 households that were in the program; i. Twenty-five households were able to provide estimates of the roof area contributing to their rainwater collection system. For each of these households, the total volume of rain falling on the contributing area was estimated by multiplying contributing area by daily rainfall depth recorded at a nearby facility for the days the system was in use.
Rainfall capture efficiency was defined as the ratio of total volume of rainwater used relative to the total volume of rain that fell on the contributing roof area. Each household has a unique rainfall capture efficiency, based on the combined influences of system storage capacity, frequency of system use, and the pattern distribution, intensity, etc. The efficiencies of both groups improved in relative to , which might be explained by a difference in rainfall patterns between the two years or might indicate a learning curve as participants get used to system operation.
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As a final observation, the two households with modified systems and gallon systems demonstrated a relatively high rainfall capture efficiency among all the study participants. Rainfall Capture Efficiency in, and As part of a town-wide water conservation plan, in September of , the town of Reading, MA, began offering water customers free indoor water use audits and water saving retrofit devices tailor-made to the results of the audits.
The town also began offering customers rebates for eligible water-efficient appliances washing machines and toilets purchased on or after July 1, The purpose of this study was to evaluate the effectiveness of these two programs at reducing town-wide water demand and the water demand of those households who chose to participate in either or both programs. Only winter water use data were evaluated to isolate indoor water use and eliminate the confounding effect of year-to-year weather variability on water use during the irrigation season.
Participants in the same category should not be interpreted to have exactly the same level of participation. For example, the numbers of low-flush toilets for any two households in the group RT may be different, and the number of retrofit devices installed among households in the group AR is variable.