Not in the same ballpark. Chernobyl nearly poisoned the entire continent’s water supply. Nuclear waste is far far worse than excess water.
Cumulative total number of deaths from Chernobyl, definitively the worst nuclear disaster in history, ranges from 4000 to 16000 (estimates, via Wikipedia). A dam bursting upstream of a few small towns will kill many more[0].
Do not underestimate excess water.
Most of Europe drinks water from underground aquifers, which could not be affected by Chernobyl. Even breathing with air with radionuclides from Chernobyl in far distance from Chernobyl power plant didn't cause much radiation dose to the population. It was eating contaminated food and drinking contaminated milk that cause most radiation dose for population.
The precise mechanism was: radioactive particles fall to ground, or are washed to ground by rain, which concentrates them on vegetation with a lot of surface especially leafy vegetables, grass. Leafy vegetables are eaten directly by humans. Grass is eaten by cows, which again concentrates the radionuclides in milk. Humans drink milk, eat cheese concentrated from milk.
Not all radionuclides produced in nuclear fission have the same health impact on population in case of a nuclear disaster. To have a significant health hazard a radionuclide needs to have 3 properties: volatility, half-life, bioaccumulativity.
Volatility - some radioactive elements (heavy metals) are not moved far away by air, some radioactive elements like radioactive noble gases dilute very fast.
Stuff with a short half-life will transform into stable elements before migrating far. Stuff with with very long half-life will not produce much radiation during human lifetime.
Bioaccumulativity, radioactive stuff needs to stay in body to do damage. If it's eaten and then pooped out next day it usually doesn't cause much damage.
Most dangerous for general public in case of nuclear disasters are:
Iodine-131 (half-life 8 days): Iodine is stored in thyroid gland and stays in for long time in body. Especially children need a lot of iodine per kilogram of body weight. In regions where there is not enough of iodine in food (lacking seafood, table salt without added iodine), human body will try to get every bit of iodine from environment and hold it in body as long as possible.
Cesium-137 (half-time 30.04 years) : Alkali metal that forms salts. Has tendency to accumulate in soft tissues.
Strontium-90 (half-time 28.91 years) : Chemically similar to calcium. Has tendency to be incorporated into bones, teeth and stay in body for very long time.
https://hps.org/publicinformation/ate/q10097/
Big part of radiation dose to the population could be prevented if the Soviet state didn't tried to cover up the Chernobyl and would prevent people from eating local food and milk, because most of the damage is done by eating iodine-131 in the first weeks after accident. Timely administration of potassium iodide tables would also help.
Chernobyl liquidators were affected with much broader range of radionuclides (radioactive stuff that did not migrate far) and with much high concentrations (radioactive stuff was not diluted much).
Direct deaths: 2 killed by debris (including 1 missing) and 28 killed by acute radiation sickness.
https://en.wikipedia.org/wiki/Chernobyl_disaster
There many estimates about impact of Chernobyl disaster. I think the most comprehensive study is from Chernobyl Forum.
"On the death toll of the accident, the report states that 28 emergency workers died from acute radiation syndrome and 15 patients died from thyroid cancer. It roughly estimates that cancers deaths caused by the Chernobyl accident might eventually reach a total of up to 4,000 among the 600,000 cleanup workers or "liquidators" who received the greatest exposures."
How would Chernobly poison all of Europe's (or you mean Asia's?) drinking water while all of our nuclear testing hasn't?