Trees on city streets cope with drought by drinking from leaky pipes

Original Article ↗ Hacker News Discussion ↗

Known phenomenon: tree roots and pipes

  • Many commenters note that trees invading water and sewer pipes is very old news; the novelty is the study’s quantified comparison: street trees show less water stress than park trees, traced to city water leakage.
  • Multiple anecdotes of roots clogging residential sewage and sprinkler lines (cast iron, clay, and PVC), sometimes causing very expensive repairs and even flooding.

Lead isotopes and tracing water sources

  • Clarification that the study’s finding relies on different lead isotope “signatures”:
    • Lead in street trees matches local lead water pipes (old, geologically distinct ore).
    • Lead in park soils/trees matches atmospheric lead from gasoline additives, whose ore sources were more centralized and globally traded.
  • Several comments elaborate how ore source, uranium/thorium content, and industrial supply chains lead to different isotope ratios that can be used as tracers.

Health and contamination concerns

  • One camp argues leaky pressurized water mains mostly leak outward, so intrusion of contaminants is rare except during depressurization events (power outages, shutoffs), which is why boil-water advisories are sometimes issued.
  • Others counter that unannounced shutoffs are common, global infrastructure is often intermittently pressurized, and contamination via rivers downstream of sewage discharges can be serious even without pipe intrusion.

Scale of leakage and whether to fix it

  • Montreal’s reported 500 million litres/day loss prompts shock and comparisons:
    • Self-reported losses elsewhere: ~20–30% typical, up to ~40–50% in some cities.
  • Debate on fixing leaks:
    • Pro-fix: leaks waste treated water, shorten pipe life by attracting roots, and indicate underinvestment and “technical debt.”
    • Skeptical/nuanced: in water-rich systems returning to the same basin, ecological benefits to trees and cooling might outweigh costs; moreover, digging up roads and coordinating utilities is enormously expensive and politically difficult.

Urban hydrology and design choices

  • Several commenters argue the real design failure is routing rainwater rapidly into storm drains instead of deliberately watering street trees.
  • Others respond that “it’s cheaper not to do it,” while some push back that short-term cost focus and fragmented incentives, not absolute cost, drive these decisions.