California OWTS Tiers
California OWTS Tiers: What “Impaired Waterway” Rules Mean for You California OWTS Tiers: What “Impaired Waterway” Rules Mean for You. Of everything in this cluster, this is the piece that applies regardless of what your soil looks like. California’s OWTS Policy — adopted by the State Water Resources Control Board in 2013 — sorts every septic system in the state into a risk-based tier, and which tier applies to your property can matter more than whether you’re sitting on clay,…