When do we stop boiling our private well water? — a lot of folks are asking.
In response to widespread flooding, a boil water notice was issued on May 24 by Hays County for residents using private wells for drinking water. The notice was posted to be in effect until further notice, so many residents are asking when their well water will be safe to drink again. The answer is: it depends.
Karst aquifers like the Edwards and Trinity aquifers recharge when there is flow in creeks that cross their recharge zones (areas where the rock layer that forms the aquifer is at the surface). During storm events, runoff can wash bacteria and other contaminants directly into the groundwater system.
Each well will respond to recharge differently. You can picture recharge like a parking garage where the rocks at the surface allow water to get down into the lower levels then travel horizontally. Many Edwards and Upper Trinity wells are very connected to surface water systems and have quick responses to rainfall events. Even the deeper wells in the Middle Trinity recharge from creek flow (out west of Wimberley where the Middle Trinity rocks are outcropped at the surface). Wells may also be open hole completions open to more than one aquifer system (like a hybrid Upper and Middle Trinity well).
Most often, well owners notice a change in taste, smell, or appearance that can be associated with an influx of surface water into the groundwater system, but that is not always true. Private well owners are not governed by the same EPA drinking water standards and treatment protocols that public water suppliers have to follow. So it is up to individual well owners to determine how/when to treat private well water. While creeks have turbid flow that is likely runoff, it is wise to use caution and either treat water (especially for bacteria–by UV or Chlorine systems) or switch to drinking bottled water.
It is not known when Hays County will lift the boil notice, but if a well owner wanted to be cautious, they could wait for the runoff to clear up and take a well water sample into a lab and have it tested for bacteria (~$20). It is recommended by many groundwater associations that 1) well owners use UV or chlorination systems to prevent bacteria problems and 2) private water wells be tested for bacteria annually or when there is a change in taste, smell, or appearance.
For more info, here are a few useful links:
· District Well Owner page (Local Water Quality Labs, Well Owner Guide, Annual Check-Up)
· EPA What to Do After the Flood (flooded wells) factsheet
· Tx Well Owner Network Solving Water Quality Problems in the Home (table of treatment systems and what they address) factsheet
· Tx Well Owner Network factsheets
· Hays County Emergency Information (boil water notice posted here)