Tex. Water Code § 5.134

(a) The commission may accept environmental testing laboratory data and analysis for use in commission decisions regarding any matter under the commission's jurisdiction relating to permits or other authorizations, compliance matters, enforcement actions, or corrective actions only if the data and analysis is prepared by an environmental testing laboratory accredited by the commission under Subchapter R or an environmental testing laboratory described in Subsection (b) or (e).

(b) The commission may accept for use in commission decisions data and analysis prepared by:

(1) an on-site or in-house environmental testing laboratory if the laboratory:

(A) is periodically inspected by the commission; or

(B) is located in another state and is accredited or periodically inspected by that state;

(2) an environmental testing laboratory that is accredited under federal law; or

(3) if the data and analysis are necessary for emergency response activities and the required data and analysis are not otherwise available, an environmental testing laboratory that is not accredited by the commission under Subchapter R or under federal law.

(c) The commission by rule may require that data and analysis used in other commission decisions be obtained from an environmental testing laboratory accredited by the commission under Subchapter R.

(d) The commission shall periodically inspect on-site or in-house environmental testing laboratories described in Subsection (b).

(e) The commission may accept for use in commission decisions data from an on-site or in-house laboratory if the laboratory is performing the work:

(1) for another company with a unit located on the same site; or

(2) without compensation for a governmental agency or a charitable organization if the laboratory is periodically inspected by the commission.