With extract-based recipes, RO, distilled, or low mineral water (some brands of spring water, some people's tap water) is often recommended (see How to Brew, 4e for details).
That water could be fine. People report good results with some brands of spring water (I use distilled/RO). Some people are able to get recent mineral analysis of brands of spring water by checking the brands web site.
With extract+based recipes, high amounts of minerals in water that's steeped 'too warm' apparently can lead to astringency. There are other probable causes of astringency as well.
If you can't find information on the mineral content for that brand spring water to confirm that it is low in minerals, one option would be to brew the same kit (ideally the same way) with distilled / RO water. It would be also reasonable to verify that the kit instructions do not contain typing errors and includes good practices for steeping.
Do you have a link to the specific recipe that you brewed?