TTHMs require quarterly reporting. This regular information submittal creates a rolling four quarter average. The District has increased optional sampling to monitor progress in the effort to reduce TTHM and to watch indicators that TTHMs may be high before they happen.
Minor fluctuations in TTHMs are normal, which is why the regulation is based on an average, rather than a single sample.
The District uses three different sources of water, including groundwater, Santa Ana River Water, and State Project Water from northern California.
Surface water only accounts for 26% of the District's water supply.