The reason bottled-water manufacturers don't advertise the product as suitable for babies is that tap-water is often far cleaner.
You are quite correct to identify filtration as assential: soil particles and 'dirt' (any visible organic matter) harbour bacteria and may shield them from boiling or chemical sterilisation. The public water supply is treated by filtration - usually sand filter beds - and by 'flocculation', the addition of chemicals that cause minerals to precipitate out of solution and small suspended particles (including bacteria) to clump and settle out. Some brands of water-purification tablets do this, too - its quite a party trick, turning ditchwater sparkling clear - and flocculation alone is often sufficient to render water safe to drink without additional chemical treatment. Nevertheless, both you and the local water authority will use a chemical agent, too - a belt-and-braces approach that leaves the smell of chlorine and a near-total reassurance that treated water is now safe to drink.
Be that as it may, floodwater is best left well alone: it isn't just soil bacteria and sewage, it's chemical pollutants you need to worry about. Runoff from roads, for example, contains oil and petrol residues - mildly carcinigenic, severely irritant to your gut. Even charcoal filtration isn't reliable against urban pollutants, and there's no hope of removing industrial spillage.
So collect rainwater instead - it still needs treating (was the container clean?) but it's a better bet than floodwater.
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The reason bottled-water manufacturers don't advertise the product as suitable for babies is that tap-water is often far cleaner.
You are quite correct to identify filtration as assential: soil particles and 'dirt' (any visible organic matter) harbour bacteria and may shield them from boiling or chemical sterilisation. The public water supply is treated by filtration - usually sand filter beds - and by 'flocculation', the addition of chemicals that cause minerals to precipitate out of solution and small suspended particles (including bacteria) to clump and settle out. Some brands of water-purification tablets do this, too - its quite a party trick, turning ditchwater sparkling clear - and flocculation alone is often sufficient to render water safe to drink without additional chemical treatment. Nevertheless, both you and the local water authority will use a chemical agent, too - a belt-and-braces approach that leaves the smell of chlorine and a near-total reassurance that treated water is now safe to drink.
Be that as it may, floodwater is best left well alone: it isn't just soil bacteria and sewage, it's chemical pollutants you need to worry about. Runoff from roads, for example, contains oil and petrol residues - mildly carcinigenic, severely irritant to your gut. Even charcoal filtration isn't reliable against urban pollutants, and there's no hope of removing industrial spillage.
So collect rainwater instead - it still needs treating (was the container clean?) but it's a better bet than floodwater.