Judgment :- Arijit Pasayat, C.J. These eight appeals are directed against the common judgment dated 20.11.1998 passed by learned single judge disposing of four Original Petitions viz. O.P. Nos. 8592 of 1990, 445, 1120 and 1970 of 1995. Four Writ Appeals have been filed by the Kerala State Pollution Control Board, Thiruvananthapuram, (in short 'the board) and four appeals have been filed by the Travancore Rayons Ltd., Rayonpuram (in short, 'the Company'). 2. Background facts are undisputed and need to be noted in brief. Company is a public limited one, manufacturing rayon and cellophane. For various purposes of the factory, water is drawn from Periyar river and is used for manufacturing, domestic purposes, generating streams etc. In course of manufacture, some quantity of water get polluted, which is treated in the Effluent Treatment Plant of the factory and treated water is discharged back to river again. For such discharge, consent from Board is necessary in terms of Water (Prevention and Control of Pollution) Act, 1974 (in short 'the Water act). Said consent is valid for three years. Condition No. 4 of the consent order indicates the tolerance limits, that is the effluent characteristic, should be within the indicated tolerance limit. 3. Water (Prevention and Control of Pollution) Cess Act, 1977 (in short 'the Cess act) provides for levy of cess on the water consumed by every local authority or specified industry. According to S.7 of the said Act, rebate cess payable would be granted if person liable to pay cess instals any plant for treatment of sewage of trade effluent. R.6 of the Water (Prevention and Control of Pollution) Cess Rules, 1978 (in short, 'the rules') allows rebate where a consumer instals any plant for treatment of sewage or trade effluent and such rebate is available from expiry of 15 days from the date on which such plant is successfully commissioned, and so long as plant functions successfully. R.4 of Cess Rules requires filing of return by fifth of every calendar month in Form No. 1. The rate of rebate is different at different points of time and we shall deal with the rates a little later. 4. Company's stand was that it has installed effluent treatment plant much before Pollution Control Act or Cess Act came in to force. The rate of rebate is different at different points of time and we shall deal with the rates a little later. 4. Company's stand was that it has installed effluent treatment plant much before Pollution Control Act or Cess Act came in to force. Plant installed in the factory is a very efficient one and is functioning regularly and effluent is discharged only after proper treatment in said plant. Company has to test the treated effluent and furnish test results to the Board along with monthly return submitted by it under R.4 of Cess Rules. Consent order granted to company mentioned nine parametres of pollutants i.e., tolerant limit and company has always been achieving 100% result with regard to seven items. There has been occasional variations in PH (acidity and alkalinity) and on very rare occasions, variation of Biological Oxygen Demand (in short 'BOD'). For last several years, according to company, there has been variation in PH or BOD on an average of five days in a month. Because of this variation, rebate to which company is entitled to, is not granted by the Board. According to it, barring those days when there were variations i.e., days when tolerance limit was exceeded, which can, admittedly, be ascertained, company ought to have been granted rebate in respect of those days when discharged water treated in effluent treatment plant and put back in the river was well within tolerance limit. In other words, it is stated, department was taking calendar month as a unit and rejecting rebate for the whole month, even if there has been occasional variations for a few days in a month. Same is contrary to provisions of the Act. Dispute relates to two periods i.e., (a) from May 1981 to November 1984 and (b) November, 1986 to December, 1994. Appeals were filed before Appellate Committee for Water Cess (in short, Appellate Committee), which rejected the appeals on the ground that even if company failed to satisfy conditions of the consent issued by Board under the provisions of S.25 of Cess Act for a few days in a month, it would not be entitled for rebate. Company challenged the said order in aforesaid Original Petitions. 5. Board took the stand that S.7 of Cess Act, as amended by Act 53 of 1991, requires that a person to claim rebate has to satisfy two conditions viz. Company challenged the said order in aforesaid Original Petitions. 5. Board took the stand that S.7 of Cess Act, as amended by Act 53 of 1991, requires that a person to claim rebate has to satisfy two conditions viz. (i) it must be shown that he has not consumed water in excess of maximum quantity prescribed in this behalf under the schedule to Act and Rules, (ii) he has not violated provisions of S.25 of Water Act or any of the standard laid down by Central Government under Environment (Protection) Act, 1986 (in short 'the Environment act). In essence, Board's stand was that mere installation of effluent treatment plant would not automatically enable a person to claim rebate. It was also pointed out that company itself had admitted that there was occasional variation in the PH (acidity or alkalinity) and on very rare occasions, variation of BOD also. This would go to show that quality of effluent discharged by company is not fully in compliance with the statutory requirements under Water Act and Environment Act. It was pointed out that maxi mum quantity that could be consumed by specified industries was prescribed by the Central Government and same would show that maximum quantity of water that could be consumed by company was 200 cubic metre per to one of fibre produced. Environment audit statement submitted by company for 1993-94 and 1994-95 goes to show that water consumption for rayon yarn was 1240 and 1142 cubic metre per tonne of produce respectively. This clearly indicated that company did not comply with first condition for allowing rebate as it had exceeded the prescribed maximum quantity of water that could be consumed by it. With regard to other point, stand taken was that even if company satisfied the terms of consent under S.25 of Water Act, even occasional variations for a few days in a month would disentitle it to claim rebate for the entire month. 6. Learned single judge, on analysing S.7 of Cess Act and R.6 of Rules, held that for a person to claim rebate has to satisfy two conditions viz. (1) unit or factory consumes less than maximum quantity of water prescribed in this behalf for any specified industry or any local authority, (ii) that such person should prove compliance with provisions of S.25 of Water Act and adhered to standards laid down by Central Government under Environment Act. (1) unit or factory consumes less than maximum quantity of water prescribed in this behalf for any specified industry or any local authority, (ii) that such person should prove compliance with provisions of S.25 of Water Act and adhered to standards laid down by Central Government under Environment Act. To find out what is maximum prescribed quantity of water, one has to see the schedule given in Rules. In the case of an industry, which comes under category of viscose rayon, maximum quantity of water permitted is 200 cubic metre per to one of fibre produced. Consumer shall be entitled for rebate under S.7 on and from expiry of 15 days from the date on which such plant is successfully commissioned and so long as it functions successfully, that is, so long as he statisfies S.7 of the Act. On facts, with reference to admitted position, learned single judge held that company exceeded the permitted quantity of consumption. It was also noted that S.3 of Water Cess Act, which deals with levy and collection of Cess, clearly provides that cess shall be leviable and collected for the purpose of Water Act and utilisation there under and same shall be calculated on the basis of water consumed by such person or local authority. Again S.7(a) of Cess Act says that a person will not be entitled for rebate if he consumes water in excess of maximum quantity as may be prescribed. Similarly, R.6(a) of Cess Rules also prescribes that to claim rebate, consumer should not exceed maximum quantity specified in schedule. Therefore, it was held that company was not eligible or entitled to any rebate 7. Learned single judge also considered the question as to the effect of occasional violation of conditions 4 and 5 of the consent granted under S.25 of Water Act. Question was whether Company would be entitled for proportionate rebate. In other words, since there was admitted variation on few days in every month, whether company would be entitled to proportionate rebate for the remaining days in the respective months. Board's stand was that rebate had reference to month and if there was variation even on any of the days of the month, rebate was not to be granted. According to company, unit was a day. Learned single judge held that unit would be day and not calendar month and calculation has to be on day-to-day basis. Board's stand was that rebate had reference to month and if there was variation even on any of the days of the month, rebate was not to be granted. According to company, unit was a day. Learned single judge held that unit would be day and not calendar month and calculation has to be on day-to-day basis. 8. Company, in the four Writ Appeals, has taken a new stand which was not admittedly raised before learned single Judge. It is submitted that proviso to S.7 of Cess Act was added by Act 55 of 1992 with effect from 26.1.1992. Similarly, proviso to R.6 of Cess Rules was added by G.S.R.311(E) order dated 28.2.1992. Therefore, it is contended, the proviso will have no application prior to 26.1.1992, because said provision was indicated to be operative from the date it came into force after its publication in official gazette. It is to be noted that originally rebate was 70% and by aforesaid amendment, rate was reduced to 25%. In essence, it is submitted, proviso which disentitles a person from rebate would operate prospectively and not retrospectively. Similar submission is raised vis-a-vis the newly added proviso to Cess Rules. Learned counsel for Board submitted that this stand is being raised for first time in Writ Appeal and same should not be permitted. In any event, it is stated, provision being one which disentitles claim for exemption has to operate retrospectively. 9. It is a cardinal principle of construction that every statute is prima facie prospective unless it is expressly or by necessary implication made to have retrospective operation, (see: Mithilesh Kumari v. Prem Bahadur Khare (AIR 1989 SC 1247) and State of M.P. v. Rameshwar Rathod (AIR 1990 SC 1849)). But the rule in general is applicable where object of statute is to affect vested rights or to impose new burdens or to impair existing obligations. Unless there are words in statute sufficient to show the intention of legislature to affect existing rights it is deemed to be prospective only nova constitutio futuris formam imponere debet non praeteritis' (a new law ought to be prospective, not retrospective, in its operation) (See New Theatre (Carnatic Talkies) Ltd., v. N. Vajrapani - AIR 1984 SC 1). Provisions which touch a right in existence at the passing of statute are not to be applied retrospectively in the absence of express enactment or necessary intendment. Provisions which touch a right in existence at the passing of statute are not to be applied retrospectively in the absence of express enactment or necessary intendment. Every statute, it has been said, which takes away or impairs vested rights acquired under existing laws, or creates a new obligation or imposes a new duty, or attaches a new disability in respect of transactions already past, must be presumed to be intended not to have a retrospective effect, (per Lopes, Q inre Pulborough Parish School Board Election, Bourke v. Nutt-1894 (1) QB 725). As a logical corollary of general rule, that retrospective operation is not taken to be intended unless that intention is manifested by express words or necessary implication, there is a subordinate rule to the effect that a statute or a section in it is not to be construed so as to have larger retrospective operation than its language renders necessary. Close attention must be paid to language of the statutory provision for determining scope of retrospectivity intended by legislature. In contrast to statutes dealing with substantive rights, statutes dealing with merely matters of procedure are presumed to be retrospective unless such a construction is textually inadmissible (see Gurbachan Singh v. Satpal Singh (AIR 1990 SC 209). As stated by Lord Denning, rule that an Act of Parliament is not to be given retrospective effect applies only to statutes which affect vested rights. It does not apply to statutes which only alter the form of procedure or the admissibility of evidence or the effect which the courts give to evidence. (SeeBlyth v. blyth -1996 (1) All. ER 524 (HL)). 10. Above being the position, proviso and the conditions incorporated by it relating to grant of rebate in terms of S.7 of Cess Act read with R.6 of Cess Rules are operative with effect from 26.1.1992 and will not cover earlier periods. In view of this conclusion, the two periods under dispute that (a) May 1981 to November 1984 and (b) November, 1986 to December, 1994 (till 26.2.1992) shall be considered in the light of provision as existed prior to 26.1.1992. Writ Appeals filed by Company are allowed to that extent. 11. So far as the four appeals filed by Board are concerned, only question that needs consideration is whether learned single judge was justified in holding that day was the unit and not month. Writ Appeals filed by Company are allowed to that extent. 11. So far as the four appeals filed by Board are concerned, only question that needs consideration is whether learned single judge was justified in holding that day was the unit and not month. For resolving this controversy, a few provisions need to be noted, S.5 of Cess Act deals with 'furnishing of returns'. R.4 of Cess Rules states that return shall be filed in Form I on or before 5th of each calendar month to assessing officer. Return is required to show the quantity of water consumed in the previous month. Assessment of cess is done under S.6 on the basis of return furnished under S.5 after making or causing to be made such enquiry as is deemed fit and after satisfying that particulars stated in the return are correct. Under sub-s.(1A) of S.6, power is given assessing cess payable in case return is not filed. S.3 deals with 'levy and collection of cess'. It is the charging section. Cess is payable on calculation of water consumed. S.10 provides for interest payable for delay in payment of cess and under S.11, penalty can be imposed for non-payment of cess within specified time. Rules are framed under S.17. As per R.4 of Cess Rules, return is to be furnished in Form I. Said Form along with its annexure reads as follows : According to learned counsel for company, had intention to treat month as the unit, there could not have been a column for 'quantity of water qualifying for rebate according to assessee.' It has to be noted that rebate is granted under S.7 on cess payable. Assessment of cess payable is done under S.6 on the basis of return required to be filed under S.5 read with R.4. These undisputedly refer to monthly returns. Further, if meter was out of order, monthly average consumption of water for previous three months of working period is taken. Here also clear reference is to unit as a month. Unit for the assessment is clearly spelt out to be a month on a reading of the statutes having relevance. Inevitable conclusion, therefore, is that under Cess Act and Cess Rules, unit is a month and not day, as observed by learned single judge. 12. Here also clear reference is to unit as a month. Unit for the assessment is clearly spelt out to be a month on a reading of the statutes having relevance. Inevitable conclusion, therefore, is that under Cess Act and Cess Rules, unit is a month and not day, as observed by learned single judge. 12. Entitlements, if any, of the company has to be worked out keeping in view our observation relating to operation of the proviso to S.7 of Cess Act and R.6 of Cess Rules with effect from 26.1.1992 by taking month as the unit. All the Writ Appeals are allowed to the extent, as indicated above.