"These Marcrist PG850 drills are without any uncertainty the best tile drill you will ever buy. For the last few years I have done on average about 25 bathroom jobs that evolve drilling into grade 5 porcelain. About 15-20 holes on each job – upwards of 500 or more holes with one drill bit! OK they are a lot more expensive than other drills but at only about 10p a hole you can’t go wrong.
I have the whole water-cooling kit from Marcrist but tend to use a bucket of water and a hand held water spray to keep the drill bit cool. Works fine if you drill in short bursts. A 8mm hole can be drilled in a couple of mins in the hardest of porcelain tiles, will also go through ceramic tiles like cutting through butter!"