30/10/2025
With the current water issues in Sedgefield, I thought this was a good time to look at what happens when high salinity water enters a septic tank system. A large number of houses in Sedgefield have such a system so this could be the next big issue if the water crisis continues.
Here’s a breakdown of how high salinity, alkalinity, and conductivity in your water can affect septic tanks and the biological processes inside them.
🧪 1. Impact on the Bacteria in the Septic Tank
Your septic tank depends on anaerobic bacteria to digest organic waste. These microbes are quite sensitive to their environment:
High salinity (4000 ppm and above) can cause osmotic stress, drawing water out of bacterial cells and killing them or severely reducing their activity.
The bacteria that survive often slow down digestion, which means:
More sludge builds up faster.
Solids don’t break down properly.
There’s an increased risk of blockages or overflows.
In short: too much salt poisons the septic system’s biology over time.
⚖️ 2. Effect of High Alkalinity (pH near 9)
A healthy septic system typically operates best between pH 6.5 and 8.
At pH 9, conditions become too alkaline, which can:
Inhibit bacterial enzymes.
Reduce decomposition of organic material.
Lead to odor problems due to incomplete digestion.
🧱 3. Effect on the Tank and Drain Field Materials
High dissolved mineral content (especially sodium and calcium salts) can lead to:
Crystallization or scaling inside pipes, filters, and outlets.
Soil dispersion in the drain field — sodium can cause clay particles to break apart and clog soil pores, which reduces drainage and causes ponding.
Reduced permeability means your soakaway could slowly fail.
💧 4. Other Knock-On Effects
If the same high-salt water is being used for laundry, dishes, or flushing toilets:
The overall salinity in the septic system keeps rising, because there’s little dilution.
Over time, the tank will behave more like a brine holding tank than a biological treatment system.
🧰 5. What You Can Do
Here are some mitigation steps if this high-salinity situation continues:
1. Minimize the inflow of brackish water into the septic tank where possible — e.g., use collected rainwater or filtered borehole water for toilet flushing if available.
2. Add bacterial boosters (like Bio-enzymatic septic additives) weekly during the high-salt period — they won’t fix everything, but can help maintain bacterial populations.
3. Avoid harsh cleaning products (bleach, ammonia, drain cleaners), as they’ll worsen bacterial die-off.
4. Monitor scum and sludge levels more frequently — pump out earlier if digestion slows.
5. If the problem persists for months, consider diverting greywater (e.g., from washing machines or sinks) to a separate filtration bed to reduce salt loading in the main tank.
Stay prepared.
