Under 30 TAC 344.50, the backflow method follows the hazard. With no health hazard, a double check valve assembly (DC) is allowed, on conditions. With a health hazard, the rule lists four methods: an air gap, a reduced pressure principle assembly (RPZ), a pressure vacuum breaker (PVB) or a spill-resistant vacuum breaker (SVB). Where back-pressure is possible as well, only the RPZ or the air gap is left.
Some site facts settle it outright. A property owner wants a fertilizer injector on the irrigation system. That one fact decides the method before anyone looks at the yard: under 30 TAC 344.51(a), before any chemical is added “by any method (aspiration, injection, etc.)”, the system must be connected through an RPZ or an air gap. A PVB is off the table, however high it sits.
Most sites take two questions rather than one fact.
Question 1: is there a health hazard?
30 TAC 344.1(16) defines a health hazard as a cross-connection or other situation involving “any substance that can cause death, illness, spread of disease, or has a high probability of causing such effects” if it reaches the drinking water. A non-health hazard is one that “will constitute a nuisance or be aesthetically objectionable” (344.1(34)). Choosing the method is the licensed irrigator’s job: 344.35(d)(4) makes the irrigator responsible for “determining the appropriate backflow prevention method for each irrigation system installation”.
With no health hazard, 344.50(c) allows a DC, on three conditions: it is tested on installation, the local regulatory authority does not prohibit it, and its test cocks are used for testing only. TCEQ’s cross-connection guide for water systems, RG-478, adds that for a non-health hazard “any of the previously mentioned assemblies may be used”, meaning the health hazard assemblies, as well as a testable double check (p. 15).
With a health hazard, the DC is out, and 344.50(b) lists four methods: an air gap, an RPZ, a PVB, or an SVB.
Question 2: can back-pressure happen?
Backflow in the rule’s sense comes from “back siphonage or backpressure” (344.1(3)). RG-478 describes backpressure as pressure downstream raised above the supply pressure “by pump, elevation of piping, steam pressure, air pressure, etc.” (p. 6), and gives a well pump as an example of something that can push water back into the supply (p. 7).
This is where the four health hazard methods split. The PVB and the SVB may be used only where “there is no actual or potential for a back-pressure condition” (344.50(b)(3)(A) and (4)(A)). RG-478 gives the reason in device terms: the RPZ “will function under both back pressure and backsiphonage”, while the PVB and SVB work “under backsiphonage only” (pp. 13 and 14). Where back-pressure is possible, the choice narrows to the RPZ or the air gap.
The conditions the rule decides for you
Some site conditions are named in the rule, and each one carries its own answer:
| Site condition | Method the rule requires | Where |
|---|---|---|
| Any chemical added (aspiration, injection) | RPZ or air gap | 344.51(a) |
| Components treated with chemical additives | RPZ | 344.51(b) |
| A second water source connected to the system | RPZ or air gap | 344.51(c) |
| Property served by an on-site sewage facility | RPZ (the system “is designated a health hazard”) | 344.51(d)(2) |
| Reclaimed water used on the site | air gap or RPZ on the domestic potable line | 344.65(4) |
| Health hazard, no back-pressure possible | air gap, RPZ, PVB or SVB | 344.50(b) |
| No health hazard | DC, unless the local authority prohibits it | 344.50(c) |
Two rows name the RPZ alone, with no air gap beside it: components treated with chemical additives, and a site on an on-site sewage facility. Those two are easy to answer with “RPZ or air gap” by habit. The Backflow practice questions ask about conditions like these as short site facts.
The rule explains one row itself. Under 344.51(c), connecting more than one source “presents the potential for contamination of the potable water supply if backflow occurs”.
Which assembly can go below ground?
Only one assembly in the rule comes with below-ground instructions: the double check. 344.50(d) asks for plugged test cocks, threaded, water-tight, non-ferrous plugs, and clearance all the way around for testing and repair. The RPZ goes the other way: 344.50(b)(2) puts it at least 12 inches above ground, where it will not be submerged, with drainage for whatever the relief valve discharges. The PVB and SVB carry their own height rule above the downstream piping.
A Y-type strainer is no longer one of the double check’s below-ground requirements. The amendment that took effect on July 26, 2020 removed it (quick reference guide, p. 20).
Is the atmospheric vacuum breaker still allowed?
Not under 30 TAC 344. Since July 26, 2020 the fourth health hazard method in 344.50(b) has been the SVB, and the atmospheric vacuum breaker (AVB) appears nowhere in the chapter. RG-478 notes that an AVB “cannot have a control or shutoff valve downstream” (p. 14), and TCEQ’s quick reference guide to the 2020 changes says AVBs “will not function correctly with a downstream valve” (p. 18).
One table still names it. The public water system rules, 30 TAC 290.44(h), require protection where a contamination hazard exists, with the type of assembly “determined by the specific potential hazard identified in” 290.47(f), Appendix F. RG-478 prints that table as text (p. 50), and its row for “Irrigation systems” reads: with chemical additives, health hazard, RPBA; without them, non-health, “DCVA, AVB,or PVB”. Appendix F is written for the water system. The irrigator’s own rule is Chapter 344, and Chapter 344 lists no AVB. Each non-health row of its internal protection list is marked for a note: “Where a greater hazard exists (due to toxicity or other potential health impact) additional area protection with RPBAs is required”.
After the choice: testing and local rules
An air gap is a separation, not an assembly. Every assembly is tested by a licensed backflow prevention assembly tester on installation, repair, replacement or relocation, and every year where the system is designated a health hazard (344.50(e)). RG-478 puts the split plainly for irrigators: a licensed irrigator may install the assembly, but “it must be tested by a licensed BPAT upon installation” (p. 29). Local rules can add to all of this, and the rule says so in 344.50(c)(1): the double check is allowed only where “a local regulatory authority does not prohibit” it.