Urban heat island (UHI) countermeasures are of growing interest for cities. Field studies of micro-climatic effects of such countermeasures are scarce, yet are essential to properly evaluate the effectiveness of anti-UHI policies. One measure which has been thoroughly studied in the field is pavement-watering. The standard approach to quantifying its micro-climatic effects is to focus on the difference in measurements made at case and control stations, tacitly assuming that under normal conditions measurements made at both sites are equal. A field study of pavement-watering was conducted in Paris, France over the summers of 2013 and 2014 at two sites, one watered over its whole width and the other only over one third. Analysis of the field measurements of 1.5- and 4-m air temperature and relative humidity, mean radiant and UTCI-equivalent temperature reveal that the assumption of null interstation differences is unfounded. The standard approach is therefore ill suited to evaluate pavement-watering effects. An approach based on a two-sample t-test of the difference between watered and reference day interstation means was conducted. In the case of full-street-width watering, pavement-watering effects had statistically significant daily effects, while only 1.5-m relative humidity was significantly affected in the case of one-third-street-width watering. Watering was found to reduce maximum daily heat stress, while having smaller-amplitude statistically significant effects at night, thus slightly reducing UHI intensity. Statistically significant effects occurred most often at night for all parameters except relative humidity, which was most affected during the day. The greatest effects were reached during the day for all parameters with reductions of 0.79°C, 1.76°C and 1.03°C for air, mean radiant and UTCI-equivalent temperatures and a 4.1% increase in relative humidity. The methodology developed is not specific to pavement-watering and can be applied to the field evaluation of any UHI countermeasure.