I have actually never use water crystal before, do they actually get consumed by the roaches? I thought they just suck the water out of it, so you just keep adding water.I get a small bowl of water crystals to last about 10 days with a 1000 count lateralis colony by putting a 12 oz plastic bottle full of water in the crystals with a 1/2" diameter hole at the bottom. Make sure the cap is on tight. It slowly seeps out as the crystals are depleted and it makes it last a lot longer. It's essentially a cheap homemade water dispenser. Eventually the roaches stop eating the crystals and drink the water between them, so the risk of drowning is still minimal. In your case you could use a bigger bowl/bottle and if your colony isn't too huge it should last for enough time.