Paragraph 4 Calculation of the ID

England and Wales

(1)

The ID must be calculated from—

F1(a)

the measured radionuclide concentrations and the dose coefficients referred to as “standard values and relationships” in Article 13, and recommended for the estimation of doses from internal exposure in the definition of “standard values and relationships” in Article 4(96), of Council Directive 2013/59/Euratom laying down basic safety standards for protection against the dangers arising from exposure to ionising radiation, or

(b)

more recent information recognised by the Secretary of State, on the basis of the annual intake of water (730 litres for adults).

(2)

Where the following formula is satisfied, it can be assumed that the ID is less than the parametric value of 0.1 mSv and no further investigation is required—

Σ_{i = 1}^{n} \frac{C_{i} (obs)}{C_{i} (der)} \leq 1

where—

“C_i(obs)” means observed concentration of radionuclide I;

“C_i(der)” means derived concentration of radionuclide i;

“n” means number of radionuclides detected.

Table 1

Derived concentrations for radioactivity in water intended for human consumption

This table includes values for the most common natural and artificial radionuclides: these are precise values, calculated for a dose of 0.1 mSy, an annual intake of 730 litres and using the dose coefficients F2referred to as “standard values and relationships” in Article 13, and recommended for the estimation of doses from internal exposure in the definition of “standard values and relationships” in Article 4(96), of Council Directive 2013/59/Euratom. Derived concentrations for other radionuclides can be calculated on the same basis, and values can be updated on the basis of more recent information recognised by the Secretary of State

(1)	(2)	(3)
¹ This Table allows only for the radiological properties of uranium, not for its chemical toxicity.
Origin	Nuclide	Derived concentration
Natural:	U-238¹	3.0 Bq/1
	U-234¹	2.8 Bq/1
	Ra-226	0.5 Bq/1
	Ra-228	0.2 Bq/1
	Pb-210	0.2 Bq/1
	Po-210	0.1 Bq/1
Artificial:	C-14	240 Bq/1
	Sr-90	4.9 Bq/1
	Pu-239/Pu-240	0.6 Bq/1
	Am-241	0.7 Bq/1
	Co-60	40 Bq/1
	Cs-134	7.2 Bq/1
	Cs-137	11 Bq/1
	1-131	6.2 Bq/1

Table 2

Performance characteristics and methods of analysis

For the following parameters and radionuclides, the method of analysis used must, as a minimum, be capable of measuring activity concentrations with a limit of detection specified below.

(1)	(2)	(3)
Parameters and radionuclides	Limit of detection (Notes 1, 2)	Notes
Tritium	10 Bq/1	Note 3
Radon	10 Bq/1	Note 3
gross alpha activity	0.04 Bq/1	Note 4
gross beta activity	0.4 Bq/1	Note 4
U-238	0.02 Bq/1
U-234	0.02 Bq/1
Ra-226	0.04 Bq/1
Ra-228	0.02 Bq/1	Note 5
Pb-210	0.02 Bq/1
Po-210	0.01 Bq/1
C-14	20 Bq/1
Sr-90	0.4 Bq/1
Pu-239/Pu-240	0.04 Bq/1
Am-241	0.06 Bq/1
Co-60	0.5 Bq/1
Cs-134	0.5 Bq/1
Cs-137	0.5 Bq/1
I-131	0.5 Bq/1

M1Note 1: The limit of detection must be calculated according to the ISO standard 11929: Determination of the characteristic limits (decision threshold, detection limit, and limits of confidence interval) for measurements of ionising radiation – Fundamentals and application, with probabilities of errors of 1st and 2nd kind of 0.05 each .

M2Note 2: Measurement uncertainties must be calculated and reported as complete standard uncertainties, or as expanded uncertainties with an expansion factor of 1.96 according the ISO Guide for the Expression of Uncertainty in Measurement .

Note 3: The limit of detection for tritium and for radon is 10% of its parametric value of 100 Bq/1.

Note 4: The limit of detection for gross alpha activity and gross beta activities are 40% of the screening values of 0.1 and 1.0 Bq/1 respectively.

Note 5: This limit of detection applies only to initial screening for ID for a new water source; if initial checking indicates that it is not plausible that Ra-228 exceeds 20% of the derived concentration, the limit of detection may be increased to 0.08 Bq/1 for routine Ra-228 nuclide specific measurements, until a subsequent re-check is required.

Annotations

Textual amendments

F1: Sch. 4 para. 4(1)(a) substituted (11.7.2018) by The Water Supply (Water Quality) (Amendment) Regulations 2018 (S.I. 2018/706), regs. 1(1), 2(14)(a)
F2: Words in Sch. 4 substituted (11.7.2018) by The Water Supply (Water Quality) (Amendment) Regulations 2018 (S.I. 2018/706), regs. 1(1), 2(14)(b)

Marginal citations

M1: See sections 17A and 219(1) of the Act for the meaning of “licensed water supplier”. This definition is prospectively repealed by paragraph 120 of Schedule 7 to the Water Act 2014 from a date to be appointed.
M2: S.I. 2000/3184, as amended by S.I. 2001/2885, 2002/2469, 2005/2035, 2007/2734, 2010/991, 2013/235, 1387.