The Law Code of Yājñavalkya 3.1.15

3.1.15

udakagrahaṇaṃ sāhacaryād agnisaṃskārasyāpy upalakṣaṇārtham, nātrivarṣasya iti vacanāt | kuladharmāpekṣayā cūḍotkarṣe 'pi varṣatrayād ūrdhvam agnyudakadānādiniyamo 'vagamyate | laugākṣivacanād varṣatrayāt prāg api kṛtacūḍasya tayor niyama iti vivecanīyam | upetaś ced yady upanītas tarhy āhitāgnyāvṛtā āhitāgner dāhaprakriyayā svagṛhyādiprasiddhayā laukikāgninaiva dagdhavyaḥ | arthavat prayojanavat | ayam arthaḥ: yady asya kḷptaṃ dāhadvāraṃ kāryarūpaṃ prayojanaṃ saṃbhavati bhūmijoṣaṇaprokṣaṇādi tad upādeyam | yat punar luptaprayojanaṃ pātrayojanādi tan nivartate | tathā laukikāgnividhānenopanītasya anāhitāgner gṛhyāgninā dāhavidhānena ca apahṛtaprayojanatvād āhavanīyāder api nivṛttir iti || agnyantaravidhānaṃ ca vṛddhayājñavalkyenoktam |

The mention of 'water' is also an indirect indication of the cremation rite, owing to association, because of the statement "not for one under three years." Even if tonsure is postponed in consideration of family tradition, the obligatory rule of offering fire and water is understood after three years. From the statement of Laugākṣi, it is to be discerned that the rule of those two applies even before three years to one whose tonsure has been performed. 'If he has undergone sacred thread initiation,' that is, if he is initiated, then 'according to the ritual of one who has maintained the sacred fires,' by the method of cremation of one who has maintained sacred fires as established in one's own Gṛhya and other texts, he must be cremated with secular fire alone. 'As far as relevant' means having a purpose. The meaning is this: if an established purpose in the form of an action by means of cremation is possible for him, such as examining and sprinkling the ground, that is to be adopted. But that whose purpose has vanished, such as the arrangement of sacrificial implements, ceases. Similarly, because their purpose is removed by the rule of secular fire and by the rule of cremating an initiated person who has not maintained sacred fires with the domestic fire, the āhavanīya and other fires also cease. And the rule of another fire has been stated by Vṛddha-Yājñavalkya: