Editor of Aegus : I have just learned that the Citizons' Commit tee on water supply, at a rcoent meoting, passet a resolutiou indorsing tlio llolly systcní, and proposing to ue the water at the Bunker pow er below tho city, filtering (strainiug) tlic I ttti through a gravel bed by digging a weU near tho bank of the fiveríind pumping tlicreírora, throw ing thê water diréctly upon tho streets for uso Without offering any oommenta upon tlio Holl} sjsí.m, so-calle.], ] desira to malee a íew suggestions on tho subject oL íilt.ration. I do so at the risk of being ao scientfic as tubo unintelligible to same of the cominitteo, v.uu profesa to ha e ao íuith in BCienoe or BCÍentifto skil!. What then is tho object and what ifl aocompUshed by íiltration ? Nearly all íornis of natural water contain certain impunties ; sumo held iu solution, some in suspension; some organic and some inorganic. Clay, saud, and suoh liko articlas are held in suspension aad will be separated by straining; hIlíK; tho salta of lime, maghesia, and organio matter generalij aro heldin solution, and mil not be soparated by strain.üxg or tiltration únicas certain eonditions aro obsorved. It is acknowlodgod by all modern authors that tho prosence or absence of dissolved organic matter is he groat desiderátum in the. selection oi water for domestic fotgo Wutts, in his recent very exhaustivo wo'k cu Chemistry, remarks as follows : " The píesenos of dissolveil organio tubstance in water has probiblv a nnich greater influonco iu deterinining its fitness for dietetic purposes than eithor the imount or nature of tho saline contents of ordinay fresh water. 'J'lñs is aspeoially the case iisreardsthe water of well3 or rivera so sitaated Jiat the drainage or sowago of towns passes mío hem When this takes placo to ny cousk;. alile xtent, the natural process of puriticatiou of rivr watei', conststing in the o.vydaHon and deatrwhion of the organic substance, is not sufiiciont to ender tho water of such streams fit for domestie se near the places where the sewage of large opulations, or the drainage of factories is dishargee into tliom." Muspratt in his large roik on Chemistry remarks: "AU rrver and well waters coutain more or less organic matter wliich is acknowledged to be the predisposing ause of disease. The separation of these impuïties is a problem of high scientific interest, and ne that hos engaged tlie;itU:nti mof alltheement chemists of the day." It is apparent,then,that 10 object of filtration is the dcatruction of the rganiu matter, by a procoss of oxydation, acomplished only through contact with the atïospheric air.l A gravel bed, like the one at ie Holly works in Jackson, constantly immersd in the. water, givcs no such contact, aud conequently cannot purify water of organio mattar. u lliller's Chemistry will be found tlie follow ng : " Running water is, however, endowed 'ith a Bclf-purifying power of the highest im)ortance ; the eoutinual exposure of fresïi aïü aces to the atinosphore proniotes the oxydation f the organic matter, and if the stream is unlollutcd by the influx of the scwerage of a laiga mvD, this process is gonerally adequato to preerve it in a wholesome state." By ültration weeds, fish spawn, leaves, and finely divided ïlt or mud, are removed ; but vegetable colorng matter in solution, salts and other bodies, 'here they are dissolved, cannot be arrestad by uch ülter." We seo this same principié illusrated, quite often, in the common house filter. - Ceep it constantly ñlled with water, without acess of the chareoal and gravel to the air, and it rill cease to oxydize the organic matter or puriy. ïhere is a form of cistern filter placed in ie bottom of the cistern ; any person having ie miafortune to use this filter for a few weeks r nionths will appreciate the importance of air ontact and oxydatiou. What gave such a magc charm to the water fromtlie "old oaken buekt that hung in the well, " but the puiïfying inuence of the air in constant contact with the 'ater f What renders the water of those Wells o impure (as often to be unfit for use) ín which pumps are used but the want oL air and oxydation ? In tbc light then of common senso, common experience, and ecientific truth, ia it wise to take the water froni the "Bunker Dam " after it has received all the filtli derived from the drainage f the city and throw it directly upon the streets vith auy expectation that it will be purified by ercolation through gravel ? or would it not be etter to go above the city, pump the water into clean, pure reservoir, and if it ueed any puriyiug let it be effected by the only natural or articial process, viz. exposure to the air and oxydaïon? Lat itbe remombered that we are building works for future generationp, and thatif wo rospor as a city large manufocturing establishnents must spring up that will greatly pollute ie water of the Huron below the city, and thus Teati vr mairnifv the exiating evil.